Yūichirō Hyakuya/Relationships

Yūichirō Hyakuya was almost killed by his parents before spending time in the Hyakuya Orphanage where he met Mikaela Hyakuya and other orphans. Raised in an underground vampire city, Yu would escape and learn from Guren Ichinose that humans had survived the calamity. Unwilling to befriend others, he aspired to join the Moon Demon Company. Supervised by Shinoa Hīragi, he would help Yoichi Saotome from bullies and come into conflict with Shihō Kimizuki. Becoming a member of Shinoa's squad which included Mitsuba Sangū, he would be tasked with undermining vampires who he desired vengeance against.

After finding Mika again, Yu would be suspected of being a spy by Kureto Hīragi, where he also met Shinya Hīragi, also of the Japanese Imperial Demon Army. Working with other squads including Makoto Narumi's, Yu would battle against vampire nobles yet also find himself sought by human organisations who had practiced human experimentation. Additionally, Yu would have to work with hostile vampires such as Ferid Bathory and Crowley Eusford, where he needed their, and Krul Tepes' information after having deserted the army.

Willing to work with others if it could help his squad, Yu would be targeted by the Hyakuya Sect, yet would not fully register threats such as that from Guren due to his notion of what counted as family. Certain close ones take priority, Yu would fight against his own demon, Asuramaru when it seemed the case that he was an enemy. Yu interacts with various other characters throughout the Seraph of the End series, which affects himself and the story. This article details Yu's relationships with other characters.

Mika as a Human
At eight years old Yu met Mikaela Hyakuya when he was transferred to the Hyakuya Orphanage. Where they were the same age, Yu was invited to become a member of Mika's family in keeping with what the orphanage director taught. Although Yu was hostile from his recent experiences and rejected Mika's friendliness, even challenging him to a fight where he was beaten, Yu was still immediately welcomed into the family. Hearing Mika understand how his experiences must have been awful, Yu learned of Mika's own parental abuse.

At some point, Yu would taunt Mika with trying to gain access to the toilet he was in. Calling to Akane and the others that the bathroom was open, Yu would ignore Mika's protests.

After a virus killed the adult population and vampires emerged to take custody of the Hyakuya orphans, Yu and Mika looked after the younger orphans for the next four years, eventually creating Yu's "family." Having been taken underground, Yu and Mika once discussed what they would do if they left the vampires' city. Answering that he would like to go to paradise, Yu was confused at Mika leaving and saying that he should work hard. Angered at later learning that Mika had been going into seventh progenitor Ferid Bathory's mansion to offer his blood, Yu refused to eat the curry Mika had sent with him knowing how the ingredients were obtained. He stated to Mika he would go in his place next time. Yu was the first-person Mika shared his escape plan with having stolen a map and gun to help with this. When the escape was revealed as a trap by Ferid, he was greatly anguished at Mika's injuries and would not leave him behind. After crying that he finally had a family, Yu was pushed away for him to escape. The only survivor, Yu was haunted by this experience particularly due to him feeling that he ran away and left the others after they were slaughtered. Swearing vengeance on the vampires, Yu would suffer from nightmares on the experience where the focus was on leaving Mika behind with Ferid.

Mika as a Vampire
Four years later after Yu joined the Moon Demon Company, he met Mika once more in Shinjuku after stabbing him from behind at seeing that a vampire was trying to kill Guren. Realizing that it was Mika he stabbed, Yu was shocked and confused. Tearful at seeing him again, Yu called to see if it was really him. Surrounded by enemies and with his squad's safety at risk, Yu was pressed into retreating back with the Moon Demon Company members. Pursued by vampires and separated, Yu was picked up and carried away by Mika. Rather than hear details that he was being used by humans, Yu heeded the other words and questioned whether Mika was still human. This was asked out of guilt if Mika had been turned into a vampire because he left him. With his squad in danger, Yu would not leave them having done that before. Unconscious from his transformation he did not see Mika taken away when the vampires retreated. Afterwards, Yu's deeply entrenched hatred of vampires was never once applied to Mika. Instead, Yu was moved to tears that Mika was still alive and vowed to save him no matter what. As well as reading what he could in the library for ways to turn a vampire back into a human, Yu would also ask Guren directly if he could help retrieve Mika. In deciding that family is most important, Yu mentioned to his squad that Mika also counted. It was in Nagoya after a vampire noble extermination mission that Yu would be found unconscious by Mika. While Mika was severely injured, with help from his squad Yu was allowed to be taken by Mika for them to meet up at the airport later. After Yu woke up in a ruined convenience store, he saw how thirsty Mika was and encouraged him to drink his blood. When Mika put up a fight against it, protesting all the way through, Yu claimed that he could not live if he watched his family die once more. His methods to persuade Mika to drink was that he would cry otherwise, before expressing skepticism that Mika did not want to live by pointing out that he would have gone off and died elsewhere if he really felt that way as a method to encourage him to drink. From that angle, Yu worked on eroding Mika's reluctance to drink since there was a time limit with Mika weakened. Yu would only listen to what Mika had to say if he drank his blood and lived. Yu's blood was the first human blood that Mika drank, and he watched his eyes turn from blue to red signaling that he has finally become a true vampire. Helping to ease Mika's conflicted feelings at his change, Yu states if Mika got tired of being a vampire, then he would find a way to change him back. Largely, Yu emphasized that they would promise not to give up on living again. As his squad was in immediate danger, Yu turned to Mika for help despite his unwillingness to head back. Just as Mika done with him, Yu desired to integrate Mika into a larger family where this one needed protecting. Reaching Nagoya airport to find the Japanese Imperial Demon Army murdering its own soldiers, Yu encouraged Mika to work as a team as the worked out the means of escape. Yu would then be defended by Mika when Guren attacked. He would escape the army and vampires with Mika and spend three months near the ocean.

With Mika needing to drink and considering the bottle of squad members blood, Yu discretely placed himself beside Mika and mentions he could drink his to avoid any troubling feelings Mika may have about drinking blood. Yu appeared happy that Mika was sharing his thoughts on their next course of action with the team. When outside Ferid's mansion where Fuola Honte began attacking, Yu was distressed at Mika being assaulted. Inside, at viewing the bodies of their deceased orphanage family members, Yu was comforted by Mika holding his hand. Agreeing to practice the seraph transformation to prepare for the battle against Ky Luc, he asks Guren to not let Mika know as it was risky. Returning to the Japanese Imperial Demon Army, Yu was focused on the means to have Mika turned back into a human.

"I did find one. I have a reason to live. I have you, Mika."

- Answering Mahiru's question that he did find a reason to live as Yu takes ahold of Mika's arm.

When Mika and Yu are fighting Guren, he meets Mahiru Hīragi again. Questioned if he found a reason to his life, Yu takes Mika by the hand and says that he is the meaning of his life. Carrying Mika while retreating, Yu states for him to drink, then comments why it has to feel so good.

Attempting to reach Mika as they feel through the air, as Mika begins to perish and transform into a demon, Yu begins to cry. First, he implores Mika to drink his blood and asks the devil or god to save Mika. When Yu realizes that it is impossible to save Mika, he asks Asuramaru to kill him. Asuramaru says that Yu always considered himself a monster and if there was no one next to him who told him otherwise, then he was "empty inside", but that someone dies, implying that Mika was that person for Yu. Hearing from Asuramaru that Mika loved him and gave his life for him, Yu cries even more and says that he does not want to be alone, implying that it is without Mika that he feels alone.

On the official Japanese website, in the description of chapter 90 it was stated: "For Yūichirō, who was born without anyone who needed him, and with parents who called him a demon, Mikaela, who loved him, is the meaning of his life. If Mikaela dies, he can no longer live."

Mika as a Demon
With the energy being emitted from Mika as a demon transformation occurs, Yu clings to a signpost rather than leave. When Krul says they have to get away from the demon transformation, Yu does not want to leave Mika. Hearing that Mika will kill him, Yu only changes his mind when it is explained with that he will not be able to save him at all. Yu concentrates on how there is a way to save Mika, so promises to save him wherever he is.

"No matter where in the world you are, I'll find you and save you! So wait for me, okay?!"

- With Mika becoming a demon who could kill them, Yu leaves with Krul

When Krul raises if he seriously wants to save Mika, he kneels in front of her and entreats her to tell her how to save him. Affirming that he is his family, Yu adds that Mika's life is more important to him than his own. From Krul's thoughts that he has it just as bad, the implication is that Yu and Mika's feelings are the same towards each other, where Krul is aware of how strongly Mika feels.

After Guren announces that they are going to turn Mika into a cursed gear and tie him to Yu, he is shocked, but then hears it as that Guren will save Mika so rejoices. Enthralled with the idea that this is saving Mika, he does not seem to register Kimizuki's words that turning Mika into cursed gear would not count as saving him. When Yu sees Mika's sword, he begins to rejoice like a child and thinks Mika is there.

"My Mika."

- Yu's Mika

Later for reasons unknown, Yu hears Mika's voice calling him for help. Shouting for everyone to hurry up, Yu warns Mika is in danger then adds he will go anywhere to him and overcome whoever comes between them. When Guren says that Mika as a demon would not remember him and will take possession of his body, Yu replies that he is not against it, because it means that Mika will live. Taking ahold of Mika's sword in the activated spell circle, Yu vows to save him. When Yu reaches the world that Mika is in, he questions what the demons are doing and mentions "My Mika". Directing himself straight towards Mika who appears as a child, he fends off his own demon Asuramaru, along with Kiseki-o and Gekkouin around him.

"I can feel the power inside. Right now, my desires have gone completely berserk. Man. It feels so good... living purely for my desires. Now... let my heart shout that desire aloud... I'm saving Mika."

- Considering his desires based on saving Mika.

In dialogue with Asuramaru when a possession attempt is underway, Yu speaks that his main desire is to save Mika. Told this is a lie and he has another desire, asked why he is so fixated on Mika and what it is he has that drives him, Yu does not entertain that question and remains set on his spoken goal. Rather than engage with this conversation, Yu undergoes a demon transformation and has the backing of three seraphs to help him overcome possession with the resolve to save Mika. Later, when reconnecting with Mika, he tells him that even if the world ends tomorrow, he will still save him.

After he wakes up in an illusionary world, Yu is pleased to recognize it as where Mika returned to him in Nagoya. Finding Mika within the store, Yu happily runs to him. At being asked how he knows his name, Yu acknowledges that Mika does not remember him and his expression changes at facing a demon with no memories. When attempts to rouse Mika's memories fail, at first, Yu is fine with letting the demon eat him, but upon remembering Guren's words, Yu reconsiders that Mika will cry if he dies.

"Yeah, if I left you beat me, you'd wind up crying after. So I guess I can't let you win. I promised everyone I'd come back alive too."

- After recollecting Guren's words Yu changes from being fine with Mika consuming him to opposing it for Mika and their squad's sake.

Accordingly, Yu decides to subdue the demon by fighting who he was warned was a stronger foe. Talking about letting his desires run wild is resorted to in order to save Mika. During the battle, Yu recalls Guren's words that the only way to victory is to break the demon's heart, so Yu decides on that course of action. Although Yu does not want to hurt Mika, and indeed used words to win over Asuramaru before, Mika as a demon is stronger leaving Yu little choice practically. When Yu's heart is pierced by Demon Mika, it is seen in memories that the failed escape from Sanguinem where Mika died in Yu's arms is his greatest fear.

After ambushing Demon Mika who was perusing the memory of him, Yu sees they have the same traumas in their heart then registers that they have the same dream. After being addressed as "Yu-chan" by the demon, Yu is delighted as he thinks Mika remembers him. Hearing that this is not so, Yu states that he will make a human of Mika again, because they are family, before determinedly reiterating the intent to save him. When Yu loses the combat and his heart is entered, Mika has taken on the form of himself as a human teenager which shows this as Yu's greatest desire. Yu later appears to Mika who is being assailed by the First who has perceived him in the memory he is checking.

"Mika. Hey, Mika. It's me. Send your mind... ...back to me. If we work together... ...we can get away. Together, we can do anything. It's okay, Mika. Let's do it together. I'll devour you... ...and you devour me. That will let you become my demon."

- Appearing, to calm Mika and encourage him to become his demon to escape the First.

While he was decapitated in the illusionary world by a demon who does not remember him, the single large eye that is come across in Yu's heart does not regard Mika as an enemy, in an indication of Yu's deepest feelings. Aware that Mika is in danger due to Shikama Doji's attack, Yu begins to call him and speak words of support. With Mika under duress, Yu says "together" multiple times and adds that he and Mika can do everything as long as they are together. By the end, Yu states that he will devour Mika, and Mika will devour him, thereby allowing him to take over him.

"Sure thing! Don't worry about it. We can do anything together."

- Assuring demon Mika they can handle the danger of the First.

In a plane with demon Mika who he is happy to see, Yu asks if he has any memories before assuring him they can deal with the threat of the First. Telling him not to worry about it, Yu declares they can do anything together. With demon Mika questioning if Yu's body was to supposed to be his in a planned resurrection of Michaela, after considering the question Yu answers if he can bring Mika back to life then he does not really mind that. While Yu does not remember events from the ancient past, he does remember the past sixteen years where getting revenge for Mika was on his mind. Speaking how when he finally got him back, Yu mentions how Mika is suddenly a little kid who does not remember the last sixteen years, and he questions does demon Mika know how much of a pain that is.

"Take my hand... ...and let's be together. You become my demon."

- Using dialogue with demon Mika.

Dismissing that trouble, Yu happily states they are still alive and together so what else matters. Betting Demon Mika has the same feeling because they are family, Yu asks what does the past matter anymore. These last sixteen years are way more important to them, and Yu asks if Mika agrees while holding his hand out. Checking if demon Mika does agree, Yu then asks for him to become his demon. With Demon Mika doubting their odds of beating the First, Yu mentions their family where the desire to protect them can all be for demon Mika to devour, a means of appealing to a demon to get Mika back.

Forming the contract to have him become his demon, Yu opens his eyes to Demon Mika as his current age. Rather than discuss their future, Yu turns to the pressing matter of them dealing with the First who is working to seal them. The line of conversation is demon Mika's capabilities as a sword. Answered that Demon Mika's power depends on his wielder, after questioning if he is good as a sword form, Yu sets about assailing the First. In a combative frame of mind for the threat at hand, Yu asks Mika as a sword if they can gauge the First's power. Fine with him devouring all his power and with possessing him, Yu states ever since they joined together he has been feeling awesome. Under these conditions, at this time, Yu does use Mika as a sword, in the sense that desires for other people to love him are felt as an energy source for him, never mind their feelings for one another, while they continue to fight savagely against Shikama Doji while they can.

Turning to Demon Mika for information on the three seraphs within him, Yu is surprised they concern him. Yu changes to being thrilled at hearing that Mika has got his memories back from their shared memories involving their feelings where Yu thought why he had to go on alone. Where Yu saw Demon Mika initially as Mika, and set about saving him as part of a pre-arranged plan, to wielding him as a sword briefly where the focus was on drawing power to fight the First, with Mika back as himself Yu dwells on his feelings of happiness, to finding it hard being on his own, to being cheerful that it all worked out as he survived to meet him. Content, Yu matches Mika's words of protecting him as they returned to the physical world.

"Well you had this weird, troubled look on your face. Whatcha thinking about?"

- Attentive to Mika who as a demon has his memories back.

Among his squad, Yu focuses on Mika and takes to addressing him as "Mika-poo!" to gain his attention. Having noticed his troubled look, Yu seeks to find out if there is something on Mika's mind. In them discussing what Mika is capable of as a demon, Yu enthusiastically asks him to read his mind, and shares a toilet related memory of him attempting to access the lavatory at some point when they were children. Where Yu keeps sensitive information from others, such as denying to Guren that he wet the bed, to not wanting others such as Mitsuba looking into his past, with Mika he is completely at ease, eager to share thoughts, with nothing awkward between them.

"Oh c'mon! We can work together on a whole new level now! We should try stuff and figure out what way works the best!"

- Easing Mika who is against possessing him, and eager to work together to greater extents.

Fine with Mika possessing him when giving too much desire is mentioned, Yu is keen for them to work together on a whole new level now where they should try stuff and figure out what is best.

Speaking privately with Mika on how now is not a good time to be chatting with friends, Yu asks if he wants to join in too. Hearing Mika detail that they are involved in a plot by Guren, Mahiru, Ferid, and Krul, Yu is open to investigating this. Where Yu unequivocally trusted Guren before, he would pay heed to Mika's concerns and directly address this plot at hand with him. Not satisfied with his answer, Yu called to Mika for them to destroy the truck as promised. Fighting together, Yu would provide the desire to surpass Guren for Mika to draw upon.

Hearing that Yu needs to choose between restoring Mika or resurrecting the whole world, he initially, despite Mika's persuasion, chooses him. Immediately calling for power, Yu is prepared to fend off potential attacks from his squad.

"You're my family too!"

- Responding to Mika where Yu has armed himself against his squad who seemingly favor resurrecting humanity.

While fighting Asuramaru, who says that Mika has always been the only person Yu had eyes for, he replies that he will never give up Mika even if he has to die. In draining Asuramaru's power to be able to escape his squad, in asking Mika to help him protect his family, in practice it was asking Mika to escape with him possibly as he was the foremost important family. Together, Yu outright confirms this impression.

"Hey, Mika? This whole time I was only ever thinking about myself and my family. I just had to save my family. I just had to save you."

- Taking ahold of Mika's hand, Yu clarifies his idea of family.

Hearing Mika press him to return to his squad who said they love him, Yu rejects the idea that he left and started a new family. Becoming angry, Yu says that living in the new world with someone else and without Mika is impossible for him and that way sounds to him like telling him to go and die.

"How can you think I can start a new life... ...If you aren't in it?!"

- Anger at Mika instructing him to leave for others.

Also confiding that for four years he lived in pain and suicidal thoughts, because Mika was not around, but he survived, Yu wants Mika to praise him for it. Eventually both reconcile and decide that together they will try to save everyone, and if it does not work out, they will die together. Discussing new ventures such as forming their own goals, and potentially betraying others, Yu sees Mika as the one to discuss such courses of action with. Their past being considered the same as their present situation, Yu turns to Mika in forming a plan to resurrect humanity that not even Guren or Shikama Doji could create.

"But. There is one thing I understand. The two of us? We're still stuck in those days, Mika. We're still trapped and helpless... ...Just like we were when the vampires had us. We had way less power then than we do now... ...But you still thought your hardest. You came up with a crazy plan to get us out. You're smart. I know that better than anyone. And I know that, if you put your mind to it... ...You can come up with a plan that'll get us both out alive this time."

- Summarizing their situation, Yu regards Mika as the one to break out of it.

In planning their next steps, Yu speaks forthrightly with Mika in discussing serious topics such as attacking human settlements for resources where he more often than not seeks Miks's input in how they should proceed. Happy to offer him desires, Yu is very upfront in discussion. Even though Yu was hungry, he was happy to share his only can with Mika, but Mika refused. Thinking Mikaela is Mika, he calls him pretty. He also doesn't hesitate to talk with Mika about his lewd desires and, in which case, show them to him. After Mika tells Yu to go back to Guren and Mika himself starts to leave, Yu seems upset that Mika can leave and instantly agrees to Mika's plan. He also decides that Mika will fight with him anyway, whether Mika wants to or not.

"What kind of desires do you need me to give you then? Should I think lewd thoughts or something?"

- A forthright question for Mika.

Delighted to take Mika to Mt. Fuji, he keeps it a surprise and is impressed when he figures it out. Thinking they are about to start a battle that might get them killed, Yu would like to make some potential last memories with Mika. Maintaining high spirits when Mika feels down, Yu high-fives him as they commence the climb and enjoy discussing matters together. Set on starting the fight to save the world, Yu is keen for Mika to join him in viewing the scenary from Mt. Fuji. Asking if he is not glad they came, Yu notes Mika looks happy too.

"What? C'mon. We're gonna win this fight and live so long we'll totally forget today."

- After Mika says he will never forget the sunrise they saw together, Yu assures him of nicer times yet ahead.

Together in a cabin within the Sea of Trees, he and Mika prepare to delve into past memories together. Observing Mika disappear, Yu promptly joins him. In a memory of ancient Greece Yu has questions for Mika on why they appear as children, and where they are. Suggesting the scene of Sika Madu and his disciples, Yu gets the feeling some of Mika's memories are mixed with his.

As the First draws near, Yu and Mika cover one another's mouths. With Mika saying he was scared since they were attacked by the First before, Yu points out it was because they were really close before. Planning together, Yu heads with Mika to the First's mansion where Mikaela's body is kept. Although he can remember spending time here speaking to Mikaela, he acts as if it were Mika beside him and is surprised he does not remember.

Thrilled to be exploring memories with Mika, he feels it is like they are on an adventure together which Yu finds so awesome. Heading into further past memories, Yu turns to Mika when unsure what is at stake. Allowed the chance to compose himself, Yu excitedly speaks to Mika how their are real live dinosaurs. Unsure of the time frames, Yu questions Mika when dinosaurs were alive, and when humans came to be around.

Upon seeing Mikaela alive in the memory, Yu asks Mika since he is here does this not mean this is his memory. As Mikaela flies away, once again Yu looks to Mika to check if they can do the same. Learning from him that it is not just desire, but calories that Mika needs for his demon powers, Yu immediately returns to acquire them. Returning, Yu is enthused to resume the chase with Mika.

Keeping one another up to date to ensure they are on the same page, Yu mentions to Mika where Mikaela is headed, and is ready to run with him towards the destination. Eagerness is clear as Yu bounds through the forest with Mika towards a volcanic mountain.

At no point has Yu ever commented on Mika's tail he acquired upon his change into a demon. The first indication Yu even acknowledges it is when he is walking behind Mika and notices it has gone. Rather than make an issue out of it, Yu words it as Mika not being a demon anymore in the context of it meaning both their powers have faded where that is a concern.

"Ah. You aren't a demon anymore. I don't feel any strength, either."

- Seeing that Mika's tail has disappeared then commenting on his own power needed to traverse the memory.

Unsure why Mika has ducked once they reach the top of the mountain, Yu wonders if he lost sight of angel Mika, then whether there is something on the other side of the cliff. Sharing a look of disbelief with him, Yu processes these stark discoveries with Mika.

Keen to explore a seraph civilization with him, although they are to search for Mikaela, rather than split up Yu stays with Mika. Grinning with delight at what they are planning, Yu enjoys navigating this memory with him. When unsure, Yu questions Mika what they should do. Even when marvelling at the futuristic appearing seraph civilization that was around in Earth's prehistory, Yu's attention is brought back to what Mika is doing as they approach the First.

In viewing Mikaela interact with Sika Madu, he picks up on traits the former has that he sees in Mika. From how Mikaela is acting, Yu describes him as like a cute little puppy dog which is seen as a Mika trait. Having observed seraphs exchange their views with one another, Yu asks what Mika thinks of it.

"Hmm... Who would you back, Mika?"

- Interested in Mika's viewpoint. Yu wonders who Mika would back out of Paimon wanting others to leave him in his illness and make it to paradise, or Bael who would rather they perish together.

For what they saw in the past, Yu spoke at ease to Mika as he essentially endured an existential crisis. Unperturbed by what could be a troubling idea that they were connected to the Mikaela and homunculus named Yu of the past, Yu shared his misgivings with Mika on what the point of anything was if they were to die and forget. He also raised how he wanted to turn Mika back into a human. It was short-lived, Yu was firm that they were not the beings they saw back them, he and Mika were who they are now.

It was not just visual cues Yu paid mind to in Mika, he was also attentive to what he felt a situation was. If Mika were keeping matters to himself, Yu would breach the topic. Having picked up that Mika was at risk at becoming a full demon, Yu sought to understand what he would do.

"You can't hold for much longer though, right? The rate things are going, you'll turn into a full demon. (Mika raises how he noticed, to which Yu replies) I noticed. What'll happen when you're a full demon? Will you possess me? Or will you try to leave?"

- Raising something he noticed, before betting that Mika would attempt to leave.

For all the talk about what the point to anything was, and that things could not be changed, Yu had no doubts in his mind that there was not a reason to prevent Mika leaving should he become a full demon. Having anticipated that Mika would try to leave given the risk of possession, Yu was almost angry in asking Mika if he thought he would let that happen. A commitment to Mika was helpful in Yu's re-affirmation in not giving up on others either, where he attempted to involve Mika as well given it was Akane and others at stake.

"I'm not giving up on you."

- His concerns about his own purpose given what they saw in memories are forgotten about when Mika is his priority.

Moon Demon Company
Yu becomes a member of the elite vampire fighting unit, the Moon Demon Company, where he is in Shinoa Squad. The Moon Demon Company is a branch organization that serves under the Japanese Imperial Demon Army. His background, that he is largely unaware of himself, is known to senior members of the Japanese Imperial Demon Army. Against their methods, Yu would would find himself and his squad endangered by their activities in their quest to assert control overs vampires and other human organization. Where the Moon Demon Company itself is concerned, Yu is very close with members there, and attempts to help them after the Japanese Imperial Demon Army under Kureto Hīragi's control betrays them.

Shinoa Squad
Moon Demon Company members are divided into groups of five members each. Initially supervized by Shinoa Hīragi and befriending Yoichi Saotome, he would meet Shihō Kimizuki in the cursed gear classes, then find Mitsuba Sangū assigned as the fifth member, all under Guren Ichinose's direction.

Shinoa Hīragi
In class Yu finds Shinoa Hīragi as his appointed army surveillance officer. Monitored by her for his insubordination in the field, Yu would not initially be interested in her guidance yet finds she becomes his first female friend in the army. Yu eventually gets used to her teasing, where it is using denying or ignoring her lewd insinuations. Adhering to her directions on the battlefield, Yu is praised by Shinoa for asking whether they should retreat from vampire nobles where before he would rush into battle. When he was frustrated with his lack of capabilities even though he had cursed gear, it was Shinoa he sought clarification from.

During the battle in Shinjuku, it is the sight of Shinoa having her blood drained by Crowley that appears to factor into Yu's monstrous transformation into a one-winged being. However in this state, Yu exhibits murderous instincts and targets humans for death, namely Shinoa. The embrace by Shinoa also seems to have been responsible to some extent for Yu returning to himself. After the battle, Yu has no recollection of this happening, and out of concern checks Shinoa's vampire bite mark out of concern. Listening to Shinoa's news on how the battle was won in humanity's favor, Yu also awaited for her to to detail the situation with Mika. Happy that everyone was fine, including Shinoa, he appeared unaware of her developing feelings for him.

Summoned by members of the Hīragi Family, and piecing together that Shinoa has the same surname as the family who is in control of the army, Yu comments she is like royalty. In turning to her to help him save Mika, they take one another's hands. In discussing it as a squad, Yu shows guilt once he learns that he nearly killed Shinoa during his transformation at Shinjuku. When Shinoa is publicly scolded for her facetious attitude at the Ebina rest stop, Yu accepts the blame for them being late. In speaking with Guren about her behaviour, Yu states Shinoa is trying her best in further defence of her. In wanting to help Guren and Shinya against vampire nobles at Nagoya city hall, Yu presses Shinoa to support this course. He follows her plan despite not knowing what it is. Returning to help his squad, Yu saves Shinoa before Kureto Hīragi murders her at Nagoya Airport. Turning to her as the squad leader, Yu asks what her orders are. While Yu is against leaving Guren, it is Shinoa's words that he is not acting as himself that results in a change in plan, and they escape to the coast.

After Shinoa has brought a bottle of blood for him, where Mika addresses how humans really have been experimenting on Yu, he tries to explain that Shinoa is not one of them. Later being informed by Shikama Dōji that Shinoa is in love with him, Yu tries to save her from his influence, ignoring Asuramaru's warning. Devastated after seeing Shinoa in a comatose state, Yu forfeits his status as a former soldier and offers to be experimented on by Kureto's order. If his memories can be of help, Yu offers them as long as Shinoa is saved.

When Yu and Shinoa reunite, he does not act on what happened to her earlier, including what Shikama Doji said. Glad to see her like to the rest, they focus on escaping Shibuya which is under attack. With Shinoa and Mitsuba both inebriated, Yu puts them on his shoulders to carry them. When Shinoa blushes profusely and insists that he is not obliged to do this, Yu replies that they are all friends. Realizing that Shikama Doji has possessed Shinoa's body where Krul attacks her, Yu is worried about Shinoa. After Shinoa wakes up, Yu is thrilled at her return. Questioning if she is okay, Yu places his hand on her shoulder. Hearing Shinoa remark that she will cry if Yu dies, her words that the squad will be waiting for him are also recalled where she wished him luck. In response, Yu smiled.

Emboldened at hearing that Shinoa was assisting, Yu renewed his attack on Shikama Doji who was still a problem for her. With the First fended off, at returning to the physical world, Yu answers Shinoa he saved Mika thanks to her. Acknowledging the poison she ingested, asking how Shinoa is, Yu is concerned whether she is going to be all right. Questioned if the answer was no, would he sweep her up like a princess, Yu is startled where he is under the impression this means she is not okay. Indeed, sweeping her up off her feet, Yu carries Shinoa before expressing alarm at her having seemingly fainted. Continuing to hold her, Yu does not understand why Shinoa faked falling asleep due to his misunderstanding. Awakening in Shinoa's arms who said she could not live without him, Yu said he was sorry, he is leaving.

Yoichi Saotome
Coming across another student, Yoichi Saotome being bullied, Yu would intervene and help him. He discouraged Yoichi from joining the Moon Demon Company to avenge his sister due to his gentle nature. After heading to engage the escaped vampire, Yu found Yoichi joining him to help. After being pushed out of the window, then being saved, Yu was knocked out by an overly concerned Yoichi. As a result, Yu would find Yoichi as the one friend he makes during his brief stint of high school, the one who helps him pass Guren's criteria of progressing further. Introduced in Guren's class together, Yu would turn to seek Yoichi out as a practice partner during a mannequin training exercise, only to find he was taken by Shinoa.

Heading to acquire a black demon cursed gear, Yu agreed with the consensus of others that Yoichi was not ready. When Yoichi was indeed overcome by his demon with his mind lost, Yu was adamantly against dispatching him as ordered. Throwing down his weapon, Yu appealed to Yoichi within to return and refused to inflict harm upon his body that was being controlled by a demon. His method contributing to success, when Yoichi broke free of the demon's control, Yu found himself hugged by him before they were declared new family by Guren. Later, they both were admitted to a squad under Shinoa. Like all his other comrades, Yu treats his friend Yoichi nicely and is committed to helping him. Yu would be surprised at the swift advancement Yoichi makes with his cursed gear capabilities.

In Osaka, Yu notices Yoichi who is reacting to seeing Lacus and worries about his condition. Later, when they meet after the events in Shibuya, Yu is glad to see him like to the rest. During the ritual ceremony when a spell circle is to be formed, Yu learns that Yoichi also did poorly at school when these constructs were being taught and is happy about it. Paying attention to Yoichi's words that they are his family and do not want anything to happen to him, Yu and Yoichi, along with Mitsuba and Kimizuki, place their hands together.

Shihō Kimizuki
Crashing into Kimizuki (literally) on his first day of class for the Moon Demon Company sessions, they share that they were monitored by Shinoa. The two fight often at first and develop a rivalry, where Yu is quick to attack and is agitated further at not being as academically adept as Kimizuki is. Matched together in the mannequin training exercise, going in different directions penalizes them both. Against Kimizuki's idea of putting his exam progression before the well-being of his sister, Yu convinced him to visit Mirai. They both share strong family values for who they are close with. While Kimizuki attained his black demon cursed gear before Yu, and was another holder of one, they both acted together for common goals. In fighting Yoichi who was possessed by a demon, Yu shouted for Kimizuki to not attack to wound as he focused on getting him back.

After gaining cursed gear, Yu now considered Kimizuki as a comrade who he would protect, and a family member of their group. This does not prevent Yu from harmlessly bickering with Kimizuki, where he calls him juvenile names such as "four-eyes". They are often placed together at the forefront of battles by Shinoa, both being melee weapon wielders. Working in conjunction, they both function effectively in dealing with threats to the squad. When Yu falls unconscious after his transformation, he is carried by Kimizuki. After training with their demons, Yu is eager to demonstrate his Asura-Kannon ability against Kimizuki, before backing away from the Devil's Coffin power. Although not fighting directly, they continue to bicker.

Not undermining him in serious settings and showing trust, Yu exercises patience when Kimizuki proceeds to taunt fifteenth progenitor Lucal Wesker into attacking rather than joining with other nobles. In trying to rescue Guren, he can count on Kimizuki covering him from attacks, yet Yu was also restrained by him when the order was given to retreat. Satisfied to see Kimizuki appear when he was fighting the vampire nobles who were keeping Guren captive, Yu would regard him as some promising reinforcement. Rendered unconscious after being snared by the Devil's Coffin, Yu was transported by Kimizuki during the mass retreat to Nagoya airport.

Along with the rest of the squad, Yu resolves to help save Kimizuki's sister Mirai as their next goal after leaving the demon army together. When Ferid Bathory drains a lot of Kimizuki's blood, Yu is worried about his him and promises to get him meat. During the battle with the Sixth Trumpet, for self-motivation, Yu promises that he will save Kimizuki's sister before being helped by him to catch the youth the seraph was in control of. As a squad they travel to Shibuya together where Yu is joined by Kimizuki on the roof of the vehicle he is on.

When they meet again having fled the battle in Shibuya, Yu is glad to see Kimizuki like to the rest. Excitedly detailing to Kimizuki about what happened earlier regarding the fight between him and Mika against Guren, they decide to go and fight outside. Attacking Kimizuki in this practice match, when he is told to not to give in to him, Yu becomes more serious. Overcoming Kimizuki in the match, and witnessing his new capabilities, Yu is glad that he is getting stronger than before, rationalizing that the better each of them are, the better the overall group becomes.

After Guren arrives at their location, Yu is given a reality check by Kimizuki concerning the Lt. Colonel's words, more so given his recent actions. Although told not to believe him, Yu largely ignores Kimizuki words where he is fixed on supposedly saving Mika. He later hears Kimizuki state that he must subdue Mika and return alive. Along with Mitsuba and Yoichi, they close up hands. Even Kimizuki is cited when Yu is detailing their family to Demon Mika who has no memories. With Kimizuki coming to his setting to help fight the awakened First, Yu happily shares with Kimizuki that Mika has been saved and answers that he is strong. With the First repelled, Yu is sure to thank Kimizuki and Yoichi for coming to help.

Mitsuba Sangū
When he first hears, then meets Mitsuba Sangū outside the walls of Shibuya he learns from Guren that she is to be the fifth member of the group. While Mitsuba disliked the idea of working with newbies, Yu drew a physical response from her when he spoke brazenly of defeating vampires. After catching Mitsuba's foot aimed at his face, Yu would head on a first mission with her and the squad. Although warned of a vampire trap, Yu disregarded Mitsuba's words and intervened to save a child being chased by a Horsemen of the Apocalypse. Although with Mitsuba's help he helped deal with the threats, Yu was chastised for his actions.

Pulling Mitsuba to safety from a vampire she had not noticed, Yu protected her from possible danger. Ignoring Mitsuba's orders to leave her behind and retreat when she had been captured by a vampire, Yu took action to successfully rescue her instead. When Mitsuba questioned whether it was true that he left his family behind, Yu was against her delving into his past even when informed that he done the right thing.

In working together, with the results Yu is accepted by Mitsuba who opens up as time goes on. Mutually trusting each other, Yu battles well alongside Mitsuba and comes to reinforce her and other members of the team when they were separated in Shinjuku. Hearing Mitsuba's concerns that she was just promoted due to her family name despite not doing anything on the battlefield, Yu does not mock her. Instead, he encourages these developments where Mitsuba can use her new authority to help him get Mika. As with the other members of his squad, Yu thinks of Mitsuba as family, and is not aware of her feelings for him.

After Crowley attacks Mitsuba, he is very worried about her. When they arrive in Shibuya and Aoi Sangū is angered with Mitsuba, speaking on her behalf, Yu protects her. Affirming that he is Mitsuba's family, Yu announces he will not let anyone harm her. Yu is happy when Mitsuba thanks him. Alone with her, with Mitsuba worried that Yu is experimenting on himself having volunteered his memories, he calms her down and tells her that she should be with Shinoa.

Later, when they reunite, Yu is glad to see Mitsuba as with the rest of the squad. With Mitsuba and Shinoa very drunk, Yu lifts them onto his shoulders. Stating that they are all friends, Yu does not care if they vomit on him. Yu is surprised when Mitsuba says he will hit him if he allows Mika to take over his body.

Guren Squad
Both being Moon Demon Company squads, with Yu and Guren in particular being close, they often share the same goals and missions. The five members of Guren squad often act together where Yu has been assisted by these elite members of the Moon Demon Company on more than one occasion. They arrive to help Second Shibuya High after a vampire has escaped, and individual members are tasked with helping Yu through various means. Fighting on the same battlefield as in Shinjuku, and sparring against some at the Ebina rest stop, Yu would also be assisted by them when retreating from Crowley at Nagoya, and from the Japanese Imperial Demon Army when Kureto begins murdering soldiers. Shinoa squad that Yu is a part of and Guren squad would also join to plan and carry out an operation involving Ky Luc.

Guren Ichinose
Meeting Guren Ichinose when he reaches the outside world after escaping the vampire city, Yu is rescued by this Lt. Colonel of the Moon Demon Company and accepts his offer of revenge against vampires. Essentially raised by Guren from that point, Yu would train in sword fighting practice against him. Against making friends, Yu would also be frustrated with Guren for not letting him fight against vampires and getting his revenge as promised. Thinking of and addressing him as stupid Guren, he would also physically engage him, to little avail, in his quest to acquire the means to fight better.

Rescued by Guren after Yu fought against an escaped vampire, Yu would be permitted to attend Moon Demon Company classes after he fulfilled his criteria of making a friend in Yoichi. Weathering the effects of Guren's cursed gear sword, Mahiru-no-Yo, and taken to make a contract with a black demon of his own, Yu gained the Asuramaru sword due to Guren. Informed this was his family now, Yu was placed in Shinoa squad due to Guren arranging the team.

Answering the summons, Yu headed to Guren's location on the frontlines of the battle in Shinjuku. Reaching the location, Yu was enraged at seeing that Guren had been attacked and stabbed through the perpetrator. Registering that it was Mika, not able to carry out Guren's order to activate his cursed gear, Yu still checked Guren's state afterwards. With his squad's safety at risk, Yu complied with Guren's order to retreat from the vampires whose numbers had been bolstered with further nobles.

Finding Guren waiting for him on the path to meeting the Hiragi family, Yu was unsure what he was getting at regarding loyalty. Yu assured him that he was family who came first when the possibility of Yu cozying up to the Hiragi's was discussed. Angered after meeting members of the Hiragi family, directing his resentment at Guren he demanded his cursed gear training be increased. Even after learning that Guren might have been experimenting on him, Yu remains loyal. Knowing that time and resources could only be spared for those who were useful, Yu sought Guren's assistance in reclaiming Mika. In confirming with his squad who to stick with, Yu chose Guren as family.

Taking the blame for Shinoa after they were late to the Ebina rest stop, Yu felt the summons for punishment would just involve verbal talk from Guren. Seeing Guren's squad, Yu asks earnestly if they are his family in a casual conversation that should have been strict. Learning the true punishment was for Shinoa, he asked Guren to go easy on her, adding that she was trying her best. Speaking on this level, Yu was equally comfortable in a practice match against Guren, where he targeted him for fighting. With a spell tag placed on his head that could not be removed, Yu charges at Guren where he sought to take him down as well.

With hostages having been taken at Nagoya, Yu turns to Guren to ask if they are really going to leave them. When Crowley captures Guren, he supports helping him in the fight against vampire nobles. Against leaving Guren as instructed, Yu has to be forcibly taken away by Kimizuki and Yoichi before others are captured. Away from the fight, Yu remembers Guren's words when he was younger to continue living as someone will arrive whose help is needed. Having made up his mind, Yu disobeys orders and returns to Guren in a second rescue attempt. Disinclined to listen to commands to leave, Yu draws upon further demonic power where a demon horn emerges from his head for the first time, as he clashes with Crowley to free Guren. Gaining consciousness, Yu would ask Asuramaru what the status regarding Guren was.

Pleased to find Guren at Nagoya airport, Yu is stunned into inaction and has to be defended by Mika after being attacked. When Guren betrays Yu again, he does not believe it and continues to tell Mika that he is not dangerous despite having been stabbed. Feeling that Guren crying means he is still there, Yu attempts to reach him. With Shinoa saying Guren is not himself, among other factors, Yu has to run and leave him. When Guren attacked him, Yu thinks that Guren's demon is to blame.

As with Guren who is a Namanari, Yu receives a one-time medication to prevent his demon from taking over. Within the basement of Ferid's mansion, Yu is again thrilled that Guren has returned. Indifferent to his actions before, Yu acts to hold Mika back after he attacks while saying that Guren is family. Agreeing that Guren's plan to resurrect humanity is a good one, Yu is set on that even with the risks involved.

Having been captured by members of the Hyakuya Sect in Shibuya, and finding Guren with large demonic horns, Yu requests to be set free. Freed by Mika instead and seeing Guren with his sword drawn, Yu has no sense of danger where he is convinced Guren is on their side. Told that fleeing and regrouping with others is the way to save Guren, he shouts his intention to rescue him. Coming under attack by Guren whose power has been dramatically enhanced, Yu attempts to block what he can while escaping with Mika. Fighting alongside Mika against Guren and his demons Noya Hienma and Mahiru Hīragi, he allows himself to be partially possessed and deploys named powers of his own to battle against him.

Even with Guren's actions being responsible for Mika perishing as a vampire and becoming a demon, Yu does not feel any ill will towards him. As Yu is engulfed with the notion that Mika can be saved, where he focuses on that, Yu is willing to comply with Guren's directions to turn Mika into cursed gear after he returns. Not absorbing Kimizuki's words that turning Mika into cursed gear would not save him, Yu believes in what Guren says. When Kimizuki and Yoichi have generated their weapons to challenge Guren for his previous iniquitous actions involving their close ones, Yu remains silent.

After Guren's tearful display that he is trying to resurrect everyone, Yu is the first to happily agree to help. A combination of wanting to believe Guren, and desire to save Mika may contribute to Yu going along with what he wants. Seeing that Guren is drawing a ritual circle, Yu wants to help. Hearing that Mika is in trouble, it is Guren who Yu shouts to. Happy when he says that they will save Mika even if it is a mistake, Yu does not mind that Guren is stepping on him, and is heavily swayed by his words that family helps family.

On the rare occasion that Yu does have questions for Guren, he will go along with what he says despite his own working practices and knowledge. Even after hearing Mika's voice, and that he had made a contract with Asuramaru by speaking with him, Yu forgoes his understanding to follow what Guren said, in striking a demon to make a contract with it. With it firmly ingrained that Guren is a savior due to his upbringing, Yu happily agrees with Mika who has gotten his memories back that they should thank him together.

Having returned with Mika who is now a demon, again Yu harbors nothing negative towards Guren despite his hand in this state of being. When Guren announces they are to get into a van with Ferid, the vampire responsible for their greatest trauma, and without details of where they are heading and why, Yu wordlessly appears ready to comply.

"Hey, Guren? So what's this "grand plan" you've got in the works? Tell me everything. Ah! But hang on a sec. Before you say anything, let me say this first. I'm grateful to you. If it wasn't for you... ...I probably would've killed myself. After I watched my whole family get murdered... ...I totally lost any will to live. You saved me. I'm thankful for that. I like you for it too. And I trust you. That's how I really feel. I mean it. Now let me ask you. Answer me, yes or no. If you don't... ...I'll destroy this truck... ...and walk away."

- Upfront in raising sensitive topics such as Guren's plan, and sharing his feelings, happy all the while. Motioning for his sword while speaking, it is a new case of willing to go against what Guren wants.

After hearing Mika's concerns that they need to find out Guren's plan, Yu maintains forwardness with him by asking directly. Happy all the while as he speaks o sensitive topics, midway Yu reaches for his sword. His demeanor darkens when speaking about destroying the truck. Asking and hearing that Guren likes him, and is using him, Yu then asks whether he was in cahoots with Ferid when his family was murdered. When Guren responds about that, Yu draws upon power to clash with Guren. Angered, Yu demands yes or no answers from Guren on whether he killed his family.

Snidely commenting how Guren is so powerful, Yu shares how he is excited in this fight. Since he has not beat him once, Yu confirms he does like Guren despite his previous anger but wants more than his respect.

"I want... ...to surpass him."

- A desire for Mika to consume as Yu fights Guren.

A willingness to follow Guren's direction is not replaced with a desire for vengeance despite the suspicion that he might have killed his family, rather an empowering urge to overcome who Yu essentially sees as a sparring combatant. Refusing to yield in a bitter physical fight, Yu then declares that he needs to win against Guren so that can depend on him.

"I'm not letting go, Guren. Today... ...I finally win! Because if I don't... If I don't win.. ...You'll never lean on me! That's why I'm gonna win! I have to beat you!!"

- Determined to win against Guren to show he can count on him.

Hearing he has won against him, Yu is satisfied. Reiterating his question of whether Guren murdered his family, Yu hears yes. Considering it in anger, Yu ultimately decides to forgive Guren as he is family too, even when he is clear it was not altruistic.

"None of that matters! Because the two of us... ...Are family too! You can rely on us! So do it!"

- Dismissing Guren's actions and saying for him to rely on them.

Focusing on reconciling with Guren, he speaks for the squad to do the same. Resolved to help Guren, he is interested in hearing his plan which he regards as a weight for him. It reaches the point where Yu would trust Guren even if he lies.

"So what's been weighing on you this whole time? Can you tell us? No lies either. Got it? Well, no. Lie if you want. I'll still believe it as if it's the truth. Because I've decided you're my family!"

- Resolutely committed to supporting Guren.

After Guren delivers an ultimatum that he could choose to restore Mika and be denounced as an enemy to them, or he could resurrect all of humanity, Yu acted suddenly and drastically. In instantly meaning to fight for Mika, and deciding he would no longer do what Guren says, it is a marked departure from prior unwavering loyalty.

Despite the fact that he considers Guren important, he decided to no longer follow his plan and go his own way. However, Yu still considers Guren his family and admires him. What Guren is prepared to do is something Yu finds impressive and is evidently inspired by as he takes to forming his own plans, rather than follow what Guren wants. Where Guren may have been a savior, mentor, or something to surpass, now Yu marvels at Guren's attitude to getting what he wants.

"Guren's amazing. He's making choices. He's even willing to be the bad guy if it means getting what he wants."

- Fondly considering Guren when deciding his own path to take.

For all the times he has called Guren an idiot where it is not done in seriousness, Yu does recognize and takes into account his intellect. Ready for it, in event such as Guren attacking a truck full of supplies, Yu acts to prevent that. It is not just appreciating that Guren is intelligent, Yu seemingly also attempts to learn from him having emulated his spell tag capabilities to create illusionary copies of himself.

"Guren is smart. Give him time and he'll anticipate us coming."

- Recognizing how Guren can and likely is acting against them.

Despite this, when Yu feels threatened by Guren, he states that he will kill him if Guren follows him and Mika and launches lightning at Guren. It is implied that Yu decides to sever all ties he has with Guren and the squad. It is after witnessing memories of the past that Yu re-commits to not giving up on others. Guren is included where Yu wants to save him from what he is suffering under too.

Sayuri Hanayori
First meeting Sayuri Hanayori when he escaped Sanguinem as a child, she is one of Guren's Squad members. Years later, Yu is taught by Sayuri in class where his progress in the mannequin training exercise is also monitored by her. Heading to the black demon ceremony chamber together, Yu agrees with Sayuri's notion that Yoichi is not ready for the exercise. During the intense fighting that was occurring, Yu may not have noticed that he was on the same battlefield as Sayuri as they were repelling a vampire invasion at Shinjuku. Seeing one another at the Ebina rest stop, Yu is startled to see Sayuri and has to be reminded that she was his teacher. They would be in close proximity with one another when Yu was helped to escape Nagoya city hall, and Nagoya airport by Sayuri among other members of Guren's squad. At Ferid's mansion they prepared a battle plan for rescuing Krul and Ferid from Ky Luc, and then took part in the battle itself against him where her spell tag based weapons were of help.

Shigure Yukimi
Another member of Guren's Squad who like Sayuri was with him when Yu was found outside Sanguinem. Unknown to him, Yu was being supervized by Shigure in his first mission involving rescuing humans from a vampire lair when he was initially assigned to his squad. Called by Shigure to accept the punishment for being late to the Ebina rest stop, Yu hears from her how he should prepare for the meeting with Lord Guren. Yu would then take part in the large-scale vampire noble operation that Shigure was involved in who made use of kunai in the fight.

Mito Jūjō
Called to Mito's, and other members of Guren's squad's location at the battle of Shinjuku, they both used their close ranged combat abilities to fend off vampires. In a practice match, Yu and his squad were pitted against Mito, along with Guren and Shinya. Losing the round, Yu processed how they lost.

Norito Goshi
The subject of Goshi's illusion magic, Yu would witness a naked illusionary manifestation of himself appearing, comically crying for his mother as part of the punishment exercise directed at Shinoa. During a retreat attempt, Yu would be assisted by Goshi's illusions providing cover there, and for distracting foes that he was to target.

Narumi Squad
The five members of Narumi Squad are headed by Makoto Narumi as their leader. Another squad involved in the vampire noble targeting mission in Nagoya, they are combined with Shinoa squad, and Shinya to defeat fifteenth progenitor Lucal Wesker. After this successful mission, they would be combined further with Guren squad in a rescue operation at Nagoya city hall before they were to head to the airport. With the four members of Narumi's squad dying from a vampire ambush, and from Kureto betraying them, Makoto by himself would join Shinoa squad along with Mika.

Makoto Narumi
When Yu first meets Narumi at the Ebina rest stop, it is not on good terms. Having been late, and with Shinoa squad getting in trouble, Yu finds Narumi squeezing his hand tighter than necessary as they introduce themselves since their squads have been combined for the mission. Addressed as a kid, when Narumi was saying he was not comfortable about them having their back, Yu demanded to know how old he was anyway. Hearing that Narumi was nineteen, Yu lied in response that he was twenty. Insisting that he was not lying, Yu listened as Narumi introduced his squad. After Narumi walks away, Yu comments how that guy really got to him. Not liking the idea of someone who is older than him bossing his squad around, Yu and Narumi are very argumentative at first.

Awaiting the start of the vampire noble targeting mission, Yu has another perspective to Narumi wanting him to remember his enemy's name, that he will remember the names of those who he is to protect instead. Working with Narumi and going ahead to engage Lucal, he would help him land the finishing attack on the vampire noble before celebrating their victory. When Narumi was asked by Guren how Shinoa squad done in the mission, Yu would gleefully anticipate the praise, before beaming with delight when that was done.

Working together to free hostages tied to crosses, Yu would then head away from Narumi with his own squad to help Guren and Shinya while the release prisoners aspect of the mission was continued. After the loss of Narumi's squad, Yu with Shinoa squad would escape with him and Mika and reach the coast. Planning their next move with Yu turning into a demon for longer periods of time, Yu hears that Narumi would defend him so that his squad's deaths would not be in vain.

For the increasing lengths of time that Yu is becoming a demon, Narumi's solution is to return to the army to possibly help resolve that. While open to Narumi's ideas, Yu tells him not to bully Mika when he is suspicious that he would run away with him. As with Yu's orphanage family members, the bodies of Narumi squad are kept in storage within Ferid's mansion. With Fuola Honte's sudden commencement of an attack, Yu is defended by Narumi.

Shūsaku Iwasaki
Waiting with Shūsaku Iwasaki among other members of Narumi squad, Yu prepares for the mission against Lucal. After Shūsaku uses his cursed gear Akahebi to chain Lucal's arm, it plays a significant part in allowing them to prevail in their fight against the vampire noble. Where Yu was with Mika, he would not witness Shūsaku being murdered by Chains at Aoi Sangū's order as the seraph experiment at Nagoya airport was activated.

Rika Inoue
One of Makoto Narumi's squad members, Yu fought alongside Rika Inoue in Nagoya against Lucal where the greater numbers were an advantage. Not present at Nagoya airport, Yu would arrive after Rika was murdered for the seraph experiment.

Tarō Kagiyama
After fighting alongside Tarō Kagiyama against Lucal, the collective squads would help rescue hostages at city hall. Where Yu was unconscious and being taken away by Mika, he did not see Tarō being stabbed by a vampire where many had arrived to descend on the Moon Demon Company members.

Yayoi Endō
As with Yayoi Endō and all other members of Narumi squad, Yu had remembered their names as the ones to protect. With Yayoi about to be possibly struck by Lucal, he delivered on his words to protect them. Where he was unconscious at the time, Yu was powerless to help Yayoi when she was a casualty of the vampire ambush during the retreat to the airport.

Shinya Hīragi
While he would not have seen him, the battle of Shinjuku that Yu was in was won in humanity's favor due to reinforcements jointly led by Shinya Hīragi, the Major General of the Japanese Imperial Demon Army. Meeting him in person, Yu also learned that Shinya is an adopted member of the Hiragi family. Yu would be ordered to battle against him when Kureto suspected a traitor among them. Questioning Shinya who he was calling weak, Yu readied himself for the fight before experiencing the moveable and disappearing traits of Shinya's Byakkomaru cursed gear rifle. Even with the fiery white tiger missiles appearing in his blind spots, Yu could fend them off with his sword, yet would find himself caught off guard by the bayonet part of the weapon. Informed that he lost to a ranged attacker who was at a disadvantage in close quarters, Yu was informed that this was down to his training.

Seeing him again at the Ebina rest stop, Yu does not remember Shinya's name so refers to him as that guy from that time. In a sparring match against him, Yu is scattered by Shinya's rifle fire and comes under direct fire after targeting Guren. While Yu could cut the projectiles apart using his cursed gear, he still lost the overall fight before being spoken to by Shinya again. In the combined Shinoa and Narumi squads, Yu benefits from coverage fire provided by Shinya that wipes out many vampires on the ground in the mission against Lucal Wesker. Further support helps Yu deliver a significant attack on Lucal to collectively defeat him. In attempting to rescue Guren and him from Nagoya city hall, Yu and his squad succeed in helping Shinya escape. When Yu refuses to leave, he is made to on Shinya's orders. He hears from Shinoa that it would have been harder for Shinya to leave Guren when he is upset about that. Later on, Yu is helped to escape Nagoya with help from Shinya and Guren's squad who he is close friends with.

With him having been brought to Ferid's mansion, when Yu is practising the seraph transformation it is Shinya who he swoops down upon. They both fight against Ky Luc in the attempt to free Krul and Ferid from sunlight exposure torture.

Kureto Hīragi
With his transformation at the battle of Shinjuku, Yu helped buy time for Kureto Hīragi, the acting leader of the Japanese Imperial Demon Army to arrive with reinforcements to utterly repel the vampire invasion. Called to a meeting, Yu was warned about members of the Hiragi family by Shinoa. After finding a lone vampire within a room and vanquishing it, Yu heard from Kureto who made his presence known that this was a test to root out suspected spies in the army. A second test involved their cursed gear, where Yu was instructed to not activate his curse only to see Kureto generate the lightning based powers of Raimeiki.

As Kureto was speaking about his willingness to follow orders, Yu attempted to strike him from behind. Another test concerned Yu engaging Shinya in combat, again at Kureto's direction. Seeing Yoichi and Kimizuki bound, Yu found Kureto asking him questions where answering untruthfully would result in them being stabbed. Questioned about his Hyakuya surname, and for details involving Guren, even though Yu answered truthfully and with what limited information he had, Kureto still had Yoichi and Kimizuki assaulted. With the offer to join Kureto, the immediate response Yu gave was for him to free his friends first.

Arriving at the scene of Kureto murdering the Moon Demon Company survivors at Nagoya airport to fuel a seraph, Yu announced he was glad he came. Targeted as one of the black demon weapon holders by chains that were coming from a crate, Yu then defended Shinoa and others from Kureto's onslaught. Undergoing a seraph transformation of his own, after being identified as the Second Trumpet, the "King of Salt" Yu is ordered to be captured by Kureto. As a seraph, Yu was prevented from likely demolishing Kureto and all below after his demon Asuramaru intervened to quell the seraph's influence.

Finding him in Shibuya where Shikama Doji is active, Yu offers his own memories to Kureto and those under him to be studied. Doing this to help Shinoa who is being possessed by the First, Yu is effectively arrested and led away for the experimentation to occur.

Aoi Sangū
Kureto's aide, Yu sees Aoi Sangū with him and Shinya in his meeting. His sword blocked by hers after striking at Kureto, he is led by her for the next part of the interrogation. Seeing that Aoi is involved with murdering everyone at Nagoya airport, Yu is targeted by chains under her direction. Meeting Aoi again outside Shibuya and speaking directly to her for the first time, Yu gives an impassioned defence of Mitsuba to her elder sister.

Vampires
Having been raised in an underground vampire city, Yu harbored resentment towards vampires for having his blood taken and being powerless where he had to live as livestock. The abhorrence felt towards vampires was exacerbated after Yu witnessed his orphanage family being murdered by Ferid Bathory, where he had to leave Mika behind. Swearing vengeance against them, Yu would be consumed with hatred for vampires and spent the next four years focused solely on killing them all. Acquiring cursed gear to stand a chance at fighting these supernaturally powerful foes, Yu would undertake missions to undermine their activities and fight back against them. The hatred for vampires did not exist where Mika was concerned after he was turned into one, Yu desired to rescue him. Remaining committed to battling other vampires in keeping with army operations, Yu would also find he would have little choice but to work with hostile vampires as well. Although open to being around specific vampires, Yu still regards them as an overall threat.

"My job is to be the brawn, y'know! If any vampires show up, I'll chop 'em to bits!"

- Vampires as the first threat to come to mind.

Ferid Bathory
On their first meeting, Yu observes as vampire noble Ferid Bathory speaks with Mika. Asked if he would also be coming to Ferid's mansion, Yu gathers that Mika has been providing his blood to the seventeenth progenitor. They meet for the second time when Yu and his orphanage family attempt to escape the city, and find Ferid waiting for them at the exit. Unable to do anything due to Ferid's capacity to move extremely fast, Yu could only watch in horror as he slaughtered his family in front of him. While Yu managed to shoot Ferid in the head using a pistol that Mika had acquired, he would not know at the time that the injury is minor for a vampire. After Yu escaped he would be haunted by the nightmare of leaving Mika with Ferid, and remember him as the vampire who murdered his family.

At the battle of Shinuku, where Yu was focused on Mika and with the fighting going on he could not focus overly on Ferid. With his transformation into a monster with a desire to murder humans, Yu could also not prevent Mika being taken away by Ferid. In discussing how nobles could turn humans, Yu assumed Ferid was the one who turned Mika into a vampire.

After living on the coast with other villagers, Yu would find his location tracked by Ferid where he and his squad had to retreat since they lacked the power to fight him and Crowley. Offering a truce since the vampires had their own objectives in mind, Yu agreed he could forgive Ferid for his past actions when asked. Questioned if he really could do that after Ferid brought out Akane's head in a jar, Yu was overcome by his demon in rage and began a murderous rampage against him. While he planned with Asuramaru to be provided a level of power for a few seconds that might allow him to strike, Yu would be struck with an injection by Ferid that sealed the increasing lengths of demon possession that he was experiencing, where Yu's blood was drained as well.

Heading with him to Osaka Bay by bus with the understanding they were travelling to where the catastrophe took place, Yu accused Ferid of deceiving them upon finding many vampire nobles from abroad there. Told to be quiet for both their sakes, Yu remained silent as Ferid done the talking to third progenitor Lest Karr and second progenitor Urd Geales. Present when Ferid was sentenced to sunlight exposure torture by Urd, since he and the squad needed his and Krul's information, Yu made his way to Ferid's mansion. There, Yu learned that Ferid had stored the bodies of his orphanage family after all the years they had been murdered. Practising entering the seraph state was done with rescuing Ferid and Krul in mind, and after Yu helped free the former from Ky Luc they made their way to Shibuya together.

Located again after escaping Shibuya and the war that occurred, Yu heard from Guren that he and the squad must board the truck Ferid is driving.

Krul Tepes
Along with other surviving children, Yu was gathered by vampires under the queen of Japan, third progenitor Krul Tepes' orders after the catastrophe took place. Unaware of this, Yu also would not have known that he was seen as one of Krul's seraphs, neither be aware that a recording of his transformation at Shinjuku was seen by her at a progenitor council meeting. Similarly not knowing that it was not Ferid, rather Krul who had transformed Mika into a vampire, when Yu heard this he regarded her as the one who saved Mika's life. Feeling that Krul can be trusted, Yu holds a favorable view of Krul since she gave Mika a second chance at living.

Further details that Yu could not have known was that his cursed gear, Asuramaru, was sensed by Krul. When Yu meets Krul for the first time, it is when Mika is transforming into a demon. Where she is calling to Ashera who is within Yu, he speaks as himself and tells her to shut up since she wanted to get away from Mika. Warned that the emerging demon will kill them, Yu does not believe Krul's words that he will harm them. As soon as Krul speaks that they can save Mika, he begins to obey her. Also learning that she is Asuramaru's sister, together they escape from Shibuya. When Krul falters due to a sound that affects her, Yu takes to carrying her.

A past Yu living during the dark ages of Greece as a child was acquainted with Krul Tepes when she was a vampire then and he was still under Shikama Doji's tutelage. Curious as the what she was looking at, Yu was treated warmly by her. Asked if he could keep a secret as they were in Michaela's chamber, Yu agreed he could before asking what a secret was.

Presently, while Krul remains knocked out, Yu convinces the entire Shinoa squad that she can be trusted. Concerned that Krul has abruptly disappeared, Yu thinks how she promised to help him save Mika. Calling Krul a friend because she was the one who saved Mika in Sanguinem, Yu believes this further because she is Asuramaru's sister. Told he is not being serious enough, Yu kneels in front of her and begs Krul to help him save Mika. Excited once more when Krul agrees, Yu reveals himself as one of the black demon holders and listens to her details that she knew Mahiru, and about the deal they made.

Crowley Eusford
Upon arriving at the gates of Shinjuku, Yu instantly recognizes Crowley Eusford as a vampire noble. After pressing Kimizuki to drive their truck into him, the squad namely Yu manages to inflict some damage on Crowley. Disarming Crowley of his sword when he appeared for Shinoa, he earned this thirteenth progenitor's interest. Finding his shoulder tapped by Crowley who appeared behind him before departing for the front lines, Yu is angered by their difference in power despite having a Black Demon weapon.

It is Crowley's arrival on the frontlines, along with Chess and Horn that prevents Yu from interacting any further with Mika after finding him again, as the human forces had to retreat. Seeing Shinoa cry after Crowley bit into her may have influenced Yu's transformation into a murderous one-winged being.

Onwards at Nagoya City Hall, when Yu learns from Yoichi that the vampire inside is Crowley, he fully agrees with Guren on the noble's strength. Although tasked with freeing hostages while Guren and Shinya engage the vampire nobles, Yu turns to Shinoa to help their commanders who have been thrown further into the city hall. Their plan ready, Yu emerges to the floor above where Crowley is stood to appear underneath him with a surprise attack ready. His sword blocked, Yu is ordered to retreat when it is evident that Crowley, with Chess and Horn, are too powerful.

Having made up his mind, Yu returns with his powers boosted to assail Crowley again in an attempt to rescue Guren from him. For all his efforts, Yu is unable to inflict anything on Crowley. Agitated at being spoken to as livestock, Yu became increasingly furious in attacking Crowley to the point where a demon horn broke out from his head. Saved from capture or worse by Kimizuki's Devil's Coffin, Yu is pulled away from the fight with Crowley.

"That's enough, Crowley Eusford! We aren't going to fight you!"

- From being wary before, Yu now ceases the fight.

When Crowley surprises Shinoa Squad in the town near the sea, Yu sees they cannot win in a fight so they surrender to him. Yu resorts to Crowley as the means to rescue Ferid and Krul whose information and help they need. Surprised to hear that Crowley too was once human, Yu heads into Ferid's manor with him. There, Yu attacks Crowley with a sword in a test of power. Informed that his family's bodies are in the celler, Yu heads down there with Crowley. In training to fight with the seraph power, Yu was to have Crowley cut his arms and legs off if he goes out of control. During the attack on Ky Luc to rescue Ferid and Krul, he fights with Crowley on their side.

Chess Belle
A seventeenth progenitor, Chess Belle is seen by Yu when she arrives to reinforce Crowley outside the entrance to Shinjuku. While they prepare to fight, Yu and his squad's lives are likely spared when Chess is not even interested in fighting them. Seeing Chess biting Mitsuba, among other vampires assailing his squad, appears to have been a factor in Yu's transformation into a one-winged monstrosity that went berserk. Encountering her again at Nagoya city hall, Yu would recognize Chess. Unable to overcome Chess in combat, in blocking her weapon Yu would find himself pressed into the ground with the force to crush it. His escape from her covered by members of Guren squad, having to retreat, Yu would return and partially transform into a demon in a renewed attack on the nobles holding Guren captive which included Chess.

Horn Skuld
Like Chess, Horn Skuld is also a seventeenth progenitor and one of Crowley Eusford's aides. Fighting her on more than one occasion, Yu despite his best efforts would largely be ineffective in a battle involving Horn who would fight along with Chess and Crowley. Witnessing Horn drinking from Kimizuki as well as other vampires biting his squad may have factored into Yu's transformation.

Lucal Wesker
From intel provided, Yu is informed that Lucal Wesker is a fifteenth progenitor who frequents the park in Nagoya. Not bothering to remember his name, Yu refers to him as that “Loo-loo la-la guy”. Along with his own Shinoa squad, and Narumi squad with Shinya, they are to defeat Lucal in a combined large scale mission to destroy vampire nobles. With the mission underway, Yu is the first to engage Lucal. Throughout the battle, Yu hears he was targeted from the start, yet can count on his squad for defence. Playing a decisive role in vanquishing Lucal, along with the others Yu celebrates the defeat of the first noble vampire, where they also had no casualties.

Lest Karr
A third progenitor, once Lest Karr had arrived in Japan form Europe, Yu was in the same vicinity when he called to Ferid.

Urd Geales
One of the two second progenitors, Urd Geales was at the head of a gathering of foreign vampire nobles that Yu observed in Osaka Bay. While they did not interact, in sentencing Krul and Ferid to sunlight exposure torture, Yu's next course of action in organizing their rescue was a result of Urd's decision.

Ky Luc
The fifth progenitor Ky Luc was the target of Yu and all with him as he was tasked with guarding Krul and Ferid. Accordingly, Yu would train to exercise control over the seraph aspect of him for the first time to increase the odds of their success. When the moment came, Yu partially in his seraph state could retain his mind to engage Ky Luc. A razor sharp tongue which came came close to slicing Ky Luc's head right off, to enduring a strike meant for Guren that punctured a hole in Yu's chest were some of the abilities he could resort to. The efforts somewhat successful, Yu contributed significantly to Ferid being freed, before Ky Luc retreated with Krul still restrained. The aftermath from battling Ky Luc involved Yu having to recover in a tank where his one seraph wing was still present.

Fuola Honte
With Fuola Honte suddenly bursting out the doors of Ferid's Mansion, seen as a human, Yu and his squad would immediately be attacked. Learning that Fuola was a tenth progenitor breaches the topic how Crowley's thirteenth progenitors status had been a front.

Demons
Finding that Demons are bound to Cursed Gear weapons, Yu would come into contact with one and realize the illusionary world he had been brought within. Breaking free of the demon's possession attempt, Yu would also seek to make a contract with a black demon for the strongest type of cursed gear. With such weapons being vital in the fight against vampires since they grant dramatically enhanced capabilities, Yu would draw upon their power while also attempting to not be possessed by what was bestowing it to him.

Asuramaru
Bound to a cursed gear katana sword, Yu comes into contact with Asuramaru during the cursed gear contract ceremony. After he takes the form of Mika to taunt him with his deepest fears, familiar with the tactics, Yu speaks about acquiring power. Impaled with shadowy like spears, with illusions of Akane and other orphans speaking to guilt him, in his desire for vengeance, Yu manages to form a contract with Asuramaru verbally where he becomes his cursed gear. Until Yu weakens the curse binding, Asuramaru promises to become his friend. Given nightmares involving how Mika was left behind every night, Yu is to resist being worn down to prevent Asuramaru from taking over his body.

As well as being provided power when Asuramaru's name is invoked, Yu also receives information that a part of him is not human. While training, Yu is presented with memories of his parents attempting to murder him, yet Yu's desire to acquire power to save others such as Mika is effective for overcoming that. In resisting the allure of a seraph trumpet, Yu relies on Asuramaru's power in fighting against stronger vampires. During his rescue attempt of Guren, he is encouraged to become a complete demon. Asking what became of that attempt, it is Asuramaru's words that another member of his family is here today that causes Yu to awaken to find Mika.

After the battle in Nagoya, Yu is chained to a wall and appears with fangs and horns. With the wish of getting free, Yu appears heavily influenced by Asuramaru's complete control over his body. When Yu tries to talk about Asuramaru's memories, he hears that every time his seraph is out of control, where his body and heart gets destroyed, Asuramaru starts regaining his memories little by little. Yu learns that Asuramaru may have had a sister whom he regrets abandoning. After Yu is captured by an agent of the Hyakuya Sect, in his mind he has been struck by two long spear-based weapons resembling Jigenso yet Asuramaru nearby suddenly finds it odd for his memories to be returning.

During the Dark Ages of Greece, when Ashera was a human and enslaved, Sika Madu brought a slave named Yu to free him. Acting as a child would, while Yu's mannerisms were regarded as odd he tried to befriend Ashera, such as being keen to play with him. That Yu had seraph powers at the time was seen by Ashera. Enraged, Yu stabbed into Ashera where his own blood got into him. Where Ashera survived, Yu's blood was responsible for turning him into a vampire.

In the present day, with Yu under attack by Guren he allows Asuramaru to take partial possession of his body in order to escape and draw upon outstanding powers. When Yu sees Mika wounded, he pleads with Asuramaru to save Mika. Told he had lost too much blood, Yu was fine with being killed himself, where Asuramaru could take his body. Not flinching with a sword swung at his neck, Yu began crying once more after being reminded by Asuramaru that Mika said that he loved him. Thanks to Asuramaru's words about him, Yu finds the strength to open his eyes to Mika above.

Alerted by Shinoa that Asuramaru is a traitor working with the First, he is shocked and heads to ascertain the truth. Entering the world of Asuramaru to talk to him, Yu states that he does not care what goals he has, but warns he is not to hurt Mika.

"Hey!! What's wrong with you?! I thought you were my family!!"

- Confronting Asuramaru who was troubling Mikaela

Making his way to where Mika is situated, Yu's voice asks Asuramaru if he is really doing this and whether he is hurting his Mika. Upfront that he will kill Asuramaru and exclude him from the family if he does not stop, Yu adds he is seriously angry with him. Erupting out of Asuramaru's chest, Yu overpowers him and judges he is the enemy. Unwilling to listen to his reasons with Mika having been led away, Yu undergoes a possession attempt that he overcomes by turning into a demon, where three seraphs are also behind him. Forcibly changing Asuramaru into his cursed gear form, Yu uses him to deal with the other demons who have taken Mika.

In speaking with Mika who is a demon now how possession works, Yu mentions how if Asuramaru drew upon too much desire he risked being possessed. Not given much thought at all as Yu made his way to Akihabara, when he was attempting to escape there, his demon affected thoughts drifted to how one demon's power was not enough. Finding Asuramaru amongst a thunder struck landscape, Yu paid no mind to that, neither his last actions, and demanded power.

"Give me power. Demon."

- Seeking out Asuramaru as a demon himself when Yu desires to escape his squad at Akihabara.

The two fought, because Asuramaru was against giving Yu power. Asuramaru notices that Shikama is still manipulating Yu and asks Yu to get rid of this control. Asuramaru was the one who saw that Yu was actually looking for a way to save Mika, not everyone. Asuramaru tried to reason Yu with his friends and family and Yu agreed with this. As Asuramaru lowered his guard, Yu defeated him.

Shikama Dōji
Shinoa's demon, Shikama Dōji seems to be familiar with Yu. It transpires that in an ancient past setting, Yu as a child was with him where he had the name Sika Madu, before they freed Ashera from his enslavement. This past Yu was treated well, being fed and essentially allowed to play all day. By night though, the past Yu turned into a seraph where his head was cut off. Seen with his head back on, Yu appeared dazed and unresponsive as his stood on a throne next to Sika Madu while a black sun enveloped him. In what could be described as tests to make a seraph personality more malleable, more than one Yu was able to be created and experimented on. Able to form memories, the past child Yu learned that he had been created by Shikama to resurrect Michaela.

Although having been in a forbidden room with the corpse of Mikaela, it is the same cordial interaction when Yu is joined by Sika Madu.

"It'll be just like in those fairy tales you tell me... The prince rescuing the princess! I guess that makes me the prince, huh?"

- Fond of rescuing Mikaela and speaking candidly with Sika Madu, who he has also been told stories by.

By the present day, when Shikama Dōji invades Asuramaru's heart, Yu comes to the rescue. Tempted with details on his past, Yu denies wanting such knowledge. From a change in his eyes and physical inaction, Yu appears to be under Shikama Doji's thrall. If it were temporary or a complete ruse, Yu attacks Shikama Doji to free himself and Asuramaru. Seemingly defeating him, Yu wonders who Shikama Doji is and what he meant about him supposed to be another empty vessel.

Seeing that Shikama Doji is taking possession of Shinoa's body, Yu is surprised at the first vampire, now a demon, doing this. When Demon Mika is searching through his memories, and Sika Madu within notices him, Yu arrives to help the former. Attacking Sika Madu in the memory, Yu generates a power to strike off the First's head, before seeing him restored. Ignoring his calm requests to stop as he and Mika should not be merging at this time, Yu instead employs powers while ordering Sika Madu to die. Yu continued fighting against the First with Mika until seraphs arrived, and the First was taken by Saito's chains.

Yu refuses to follow Shikama Doji's plan any further. When Yu talks to Mika about their plans for the future, he mentions how Shikama Doji wanted to bring Mika back to life and did it without giving up. This fact makes Yu admire Shikama Doji, and comparing him with Guren, he is very impressed by that the First is willing to do.

"The First is willing to do anything to bring you back to life. He's thinking. He knows what he wants to do... ...And he knows that battles he has to win."

- Yu speaks what Shikama Doji is doing to restore Mika, and notes the lengths he would go to.

Noya Hienma
Back in the Dark Ages of Greece, the past Yu's background seemed to be known by Noya Hienma who was a vampire at the time. When a past Yu entered the room that Mikaela was kept in, that Noya along with Ashera and Krul were in, unaware that it was forbidden, he excitedly questioned whether there was a really fun toy there. Helped up to see the corpse of Mikaela within the coffin, while looking at him, Yu was murdered by Noya. It was commented by Noya that Sika Madu could make more Yu's anyway.

When Yu enters the room that seems no longer off bounds, he speaks with Noya the possibility of Mikaela being able to wake up if his name is called many times. When Noya replies that there is no chance, Yu happily keeps speaking to Mikaela who lies silent. Where he is happily asking Mika to wake up, Yu is murdered when Noya did nothing to allay his increasing irritation. When a new Yu is born a moment later from a disembodied eye in a tank nearby, he is merry and curious, where that neither his life is valued at all so is murdered by Noya. Another Yu that was formed from another eye remains silent and avoids the barbaric conduct from Noya.

In the present, when Yu has been captured with Guren standing by, he is seen by Noya who is now Guren's demon, who is surprised at a fully grown Yu. Coming under attack, Yu and Mika fight against Guren and Noya with Mahiru as well. Having escaped some distance, Yu has turned into a demon with half his mind under the control of Ashera, where they launch many swords at Noya. Another round of blades are sent to slice Noya's limbs off.

Gekkouin
The demon Gekkouin made a contract with Yoichi and powers his bow. They first meet to an extent when Gekkouin takes over Yoichi's body. After Yu states that Yoichi will never kill him because they are friends, the Gekkouin-Yoichi fusion responds he is naive. When Gekkouin tries to persuade Yoichi in his mind to kill Lacus who has been sighted, Yu notices the initial demon possession attempt and is worried. Seeing Gekkouin physically when he enters the world Mika is in, Yu attacks him as an enemy. After drawing upon demon and seraph power, Yu appears behind Gekkouin and attacks him by cutting his arm off. Then avoiding his "Thousand Arrows of Light", and "One Thread, One Glint" powers, Yu feels certain he can kill Gekkouin and Kiseki-o who is with him. Recognizing Gekkouin from Kiseki-o mentioning his name, Yu warns Yoichi that his demon is their enemy. After telling Gekkouin that he is too slow, Yu cuts him apart at the neck and waist.

Kiseki-o
Witnessing Kiseki-o's power when Kimizuki first activates the Devil's Coffin ability, Yu is afraid of it and backs away from the countdown being spoken. During the battle with Crowley, Yu is swallowed by Kiseki-o's power where the demon possession he is experiencing is rendered null. Surprised when Kimizuki receives more power from Kiseki-o where two dart firing coffins can be summoned, Yu is happy with this progression for the sake of their team. When Yu enters Asuramaru's world, he sees many of Kiseki-o's coffins around and concludes that he is also Shikama's ally. They first meet face to face in Mika's world, and Yu attacks Kiseki-o for his actions against Mika. Hit by him, Yu is certain he can defeat both Kiseki-o and Gekkouin. When his arm is clamped with a coffin, Yu reacts by cutting it off before it is reformed. Familiar with his coffins, Yu uses them to voice to Kimizuki of their demon's betrayal. Informing the demon that he is going nowhere, Yu proceeds to dismember Kiseki-o.

Mahiru-no-Yo
Guren's cursed gear sword, Mahiru-no-Yo is Mahiru and Noya combined into one being, which can also separate. After Mahiru-no-Yo's energies are emitted from the sword by Guren, as Yu could weather the effects, he was chosen to make a contract with a black demon as well. During sparring matches with Guren, it is this weapon that Yu was clashing with. During a fight to survive, Yu was stabbed through the back into his heart when the Mahiru-no-Yo sword was called.

Akane Hyakuya
Living among other orphans, Yu was closer with Akane Hyakuya compared to others where they helped look after them. As children living together in Sanguinem, Yu rejected Akane's claim that they are all a part of the same family. When she was murdered, Yu was greatly saddened over her death. At being shown her decapitated head that was kept in a jar by Ferid, he was enraged and began to go berserk with his demon. Later in Ferid's mansion, before going downstairs to see the encased corpses of his family, Yu told Yoichi that he would carry Akane's head. Once given to him, Yu then apologized to Akane for never calling her "family", and for running away. At Guren's mansion when resurrection is being discussed, Yu speaks that once he brings back Akane and the other children he will tell her they are family. That Akane would be brought back is a significant reason why Yu is comfortable with human resurrection regardless of the cost. Yu again reveals that he will resurrect Akane during a conversation with Mika. In mentioning family, Yu speaks of Akane more than others.

"Akane. The kids. Guren. Shinoa. As long as I could save the family that took me in... ...Then I didn't care about anything else."

- Akane as the first name mentioned when considering family members.

Hyakuya Orphanage Family
Living with other orphans, while Yu was not interested in the very concept of family at first, he would become a paternal figure to the Hyakuya orphans as they spent time together. Yu would miss them dearly after their passing and be troubled by nightmares of what happened, combined with the guilt that he ran away and left them.

Mahiru Hīragi
As a child Yu is visited by Mahiru Hīragi who was working with the Hyakuya Sect. While he is imprisoned and asked about the meaning of life, Yu at first tells Mahiru to go away, but she does not. Explaining to her that he is a demon spawn, having been told that by his parents, Yu is questioned why he thinks that. Although Yu's memories would be erased, he was told to stay strong and that one day, she will return to free him from the Hyakuya Sect. Eight years later, after Asuramaru finds this memory deep in his mind, Yu tells Guren that he vaguely remembers her but not her identity. He would see Mahiru's spirit once she separated from Noya and would remember who she was.

Later registering that Mahiru is Shinoa's sister and the one who created the cursed gear, Yu listens to Krul's story about the deal between her and Mahiru. They meet again when Mahiru arrives with Guren. Despite her actions before, Yu does not display any strong reactions for or against Mahiru, but is regarded by her when she is curious as to how long he has lived.

Saitō
Saved by Saitō, a second progenitor vampire from his burning apartment, Yu was then taken to the Thousand Nights. Yu is dragged to the orphanage that Mika is at on Christmas Day and told he will meet people just as unwanted as he is. Also possibly unknown, or not fully realized to him, Yu would be kidnapped by agents acting in Saito's interests when they were in Shibuya together.

Mikaela
As a child in the past, Yu knew Mikaela, who is the deceased son of Shikama Doji, since ancient times. Seeing him in his coffin for the first time, Yu immediately showed interest in him. Calling Mikaela "a pretty girl" after seeing his face, and not anything lower, Yu was then quickly killed by Noya while he was distracted. Later, Yu learned that he was created in order to resurrect Mikaela. Being a child, Yu likely could not comprehend Noya's words that this would involve him being sacrificed.

"Mika'll wake up for me! Cuz it's my job to wake him up! I was born to do it. Father told me so! So if I just call his name enough, he'll wake up! Right, Mika? You'll wake up for me, right? C'mon Mika! It's time to get up!"

- Trying to convince Noya that he can wake up Mikaela and attempting to do so by asking him.

After that, Yu began to often go to Mikaela's coffin and try and wake him up. Yu said many times that this is his goal, because he was born for this. Feeling if he called Mikaela, he would wake up for him, even when told by Noya that it was impossible, Yu continued to call for Mikaela and tried to wake him up.

By the present day, Yu finds he has memories of the ancient past and sees Mikaela as Mika. He still thinks Mikaela is pretty.

"For some reason I can remember things from before I was born. In some of the really old ones... ...I remember seeing your corpse. It was really pretty. Was that you? You even had wings."

- Describing who he sees as Mika as really pretty.

In accessing a memory, the First's mansion is reached where Yu comes across Mikaela for the first time in the present era. Happy to see the casket he is kept in, Yu expresses familiarity with him. From his wings, Yu says he must be an angel. While Yu states he remembers spending all day leaning on the casket and speaking to Mikaela in the past, what was said cannot be remembered. It is memories of Mikaela that apparently links Yu of the present day to past forms of himself. Yu recalls interacting with the casket.

"Long ago... I'd spend all day leaning on this glass."

- Expressing a familiarity with Mikaela from the ancient past.

In even earlier memories, Yu follows Mikaela as he makes his way to a seraph civilization. Consistently referring to him as the angel who looks like Mika, in his surprise at finding him again he fumbles his words to Mika. Watching Mikaela interact with Sika Madu, he tries to ascertain whose memory they are in, his own or Mika's. Comparing Mikaela to a cute puppy dog is done in the context of describing him like Mika. After witnessing his light based powers, Yu would be impressed with the capabilities shown.

"Whoa! Angel Mika's got power!"

- Amazed at the light energy Mikaela created which blew through structures.

Realizing that Mikaela meant to end his own life with a dagger, Yu spoke to the memory of him and said for Mika to not do it. In accessing memories, Yu would witness how Mikaela died. In a memory Yu witnessed the soul of Mikaela enter the body of a human who looked like him. Yu appeared shocked in saying that he was in fact Mikaela. Learning that Mikaela switched places with the homunculus named Yu so that he could not be resurrected by Sika Madu as his soul was hidden in a human body, Yu in any case affirmed that he and Mika were who they were now, and not the beings of the past.

Mirai Kimizuki
Hearing of Mirai Kimizuki's critical condition during the mannequin training exercise, Yu reminded Kimizuki to be there for his sister. When Kimizuki was seeing her in her spell tag covered bed, Yu waited nearby. Finding that Mirai had been brought to Nagoya airport and activated as the Fifth Trumpet having undergone experimentation, the devastation wrought resulted in Yu utilizing his own seraph powers to fight against Abaddon who seraph Mirai had summoned to the world. After prevailing against this threat, later Yu resolves to help rescue her from Japanese Imperial Demon Army custody. Escaping Shibuya as a squad, Yu would see Kimizuki check Mirai whose corpse was kept in a refrigerator after she was murdered by Guren for the Sinful Key within her. Where a Sinful Key had been acquired from the youth who had a seraph within him, and Mirai who had the same, Yu would not comment on this.

Sixth Trumpet
Taken to a room at Guren's residence where the Sixth Trumpet was contained, Yu entered a state where he produced a trumpet for them to communicate as seraphs. In conversing with the seraph who was speaking through a youth it was within, Yu is regarded as a defective Second Trumpet who deferred in its goal of destroying the world as he was tasked to do. Consequently, Yu is then attacked as the Sixth Trumpet wants to destroy him to have a new Second Trumpet reborn as it should be. Horsemen of the Apocalypse at various stages of formation are able to be fired at Yu by this seraph, where he can repel them.

With the being taking to the sky, Yu finds he can also produce his blackened seraph wings and employ them for flight. While the Sixth Trumpet has no desire to listen to him, Yu keeps defending from his attacks while drawing on Asuramaru's power to help do so. Discovering that the youth the seraph within also has a demon inside, Yu tackled the Sixth Trumpet to the ground where with help from Kimizuki they were able to inject him with a drug to contain the seraph and leave the human sleeping. In dealing with the Sixth Trumpet, Yu also helped put an end to the Horsemen of the Apocalypse that were being summoned to the world.

Seraphs
Coming into contact with them by one of their trumpets, Yu turns to seraphs as a source of power for challenging situations. Not concerned at their influence, where Yu is wary about demon possession, Yu ultimately has an indifferent view to seraphs themselves. Despite their very rare appearances, and that three were within him, Yu does not hold strong views for or against seraphs even where they are capable of destruction. In seeing their forms in the prehistoric past, Yu concentrated on their wings being like the First's.

"There're a whole bunch of guys who look like the First."

- Having seen them in a memory, Yu focuses on seraph's resemblance to Shikama Doji.

Walking among them in a memory, Yu concerns himself with the seraphs when it comes to thinking whether they eat. He is surprised at finding ice cream present at the time and that seraphs would apparently be interested in it.

"That's... Not what I think of when I think of angels."

- Considering ice cream given the seraphs around an area that provides it.

When human-appearing seraphs were revealed in the memory, Yu expressed familiarity with them where they do resemble demons and vampires of later eras.

"Huh... I think I've seen those angels before."

- Familiar with the humanoid appearing angels revealed.

Stepmother
As a child when his stepmother's apartment goes up in flames, she screams that Yu is a demon and should die. She then douses herself in gasoline and attempts to set herself on fire until firefighters tackle her to the ground. She succeeds in burning herself to death. Saitō later reveals that she was not his biological mother, but was his stepmother, however Yu is unaware of this.

Father
His father believes that Yu should die for the good of the world and is willing to stab and kill him to achieve this goal. but ends up dead before being able to carry this out. This experience had affected Yu, as he cries about it to Mahiru Hīragi when being held captive by the Hyakuya Sect. After making a contract with Asuramaru, he finds this memory being used to terrorize him in a nightmare. Yu felt like he died on the inside when he was treated this way by his parents.