Yūichirō Hyakuya was almost killed by his parents before spending time in the Hyakuya Orphanage where he would meet Michaela Hyakuya. Raised in an underground vampire city Yu would escape and learn from Guren Ichinose that humans existed outside. Unwilling to befriend others he was placed within the education system and aspired to join the Moon Demon Company. He was assigned to Shinoa Hīragi's squad and tasked to undermine vampires. 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.

Parents

Step-mother

As a child when his step-mother'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.[1] She succeeds in burning herself to death. Saitō later reveals that she was not his biological mother, but was his step-mother, however Yu is unaware of this.[2]

Father

His father believes Yu should die for the good of the world, is willing to stab and kill him to achieve this goal[3] but ends up dead before being able to. This experience had affected Yu, as he cries about it to Mahiru Hīragi while being held captive by the Hyakuya Sect.[4] Asuramaru later uses this memory to terrorize him in a nightmare.[3] Yu felt like he died on the inside when he was treated this way by his parents.

Hyakuya Orphanage

Mikaela Hyakuya

Yu invited to be family by Mika

At eight years when Yu was transferred to this orphanage Mika knew they were the same age and was keen to become Yu's best friend, and family in keeping with what the orphanage director taught.[5] Accordingly even though 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 in the family. Hearing Mika understand how his experiences must have been awful Yu heard Mika's account of his own parental abuse.[6]

After the virus killed the orphanage director and vampires emerged to take custody of the Hyakuya Orphans, Mika and Yu looked after the younger orphans, eventually creating Yu's "family." Yu and Mika once discussed what they would do if they left the vampires' city. Yu answered that he would like to go to paradise yet was confused at Mika leaving and saying that he should work hard.[7]

Concerned at Mika offering his blood to a vampire

Angered at later learning that Mika had been going into seventh progenitor Ferid Bathory's home to offer his blood Yu refused to eat the curry Mika had sent with him knowing how the ingredients were obtained. He stated for Mika to let himself 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.[8] When the escape was revealed as a trap by Ferid, Yu 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.[9] Yu was the only survivor and was haunted by this experience particularly due to him feeling that he ran away and left them after they were slaughtered.[10] Swearing vengeance on the vampires Yu would suffer from nightmares on the experience where the focus was on leaving Mika behind with Ferid.

Finding one another 4 years later at Shinjuku

Four years later after Yu joined the Moon Demon Company, he met Mika once more in Shinjuku after stabbing him from behind after seeing that a vampire was trying to kill Guren. However, when Yu realized that it was Mika he stabbed he was in complete shock and confusion.[11] 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 retreated back with the Moon Demon Company. Pursued by vampires and separated Yu was picked up and carried away by Mika but rather than hear that he was being used by humans Yu picked up on the words and questioned whether Mika was still human. He asked out of guilt that 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 never once entered his mind where Mika was concerned and he was moved to tears that Mika was still alive and vowed to save him no matter what. Yu searched for ways to turn a vampire back into a human[12] and would also request that his squad and then Guren as well help retrieve Mika.

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It was in Nagoya after a vampire extermination mission that Yu would be found unconscious by Mika. Whilst Mika was severely injured.[13] With help from his squad Yu was allowed to be taken by Mika for them to meet up at the airport later.[14] After Yu woke up, he saw how thirsty Mika was and encouraged him to drink his own.[15] Mika put up a fight against it, protesting all the way through, but he gave up after Yu claimed that he could not live if he watched his family die once more.[16] His methods to persuade Mika to drink was that he would cry otherwise and then expressed 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. From that angle Yu worked on eroding Mika's reluctance to drink since there was a time limit with Mika weakened. He would only listen to what Mika had to say if he drank his blood and lived. Yu's was the first human blood that Mika drank and he watched Mika's eyes turn from blue to red signalling that he has finally become a true vampire.[17] Yu helped ease Mika's conflicted feeling at his change and said if Mika got tired of being a vampire Yu would find a way to change him back. Largely, Yu emphasized that they promise not to give up on living again.

Happy

As his friends were in immediate danger Yu turned to Mika for help despite his unwillingness to head back.[18] Just as Mika done with him Yu desired to integrate Mika into a larger family where this one needed protecting.[19] Whilst he encouraged Mika to work as a team when it was clear the Demon Army was set on murdering them 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 would discretely place himself beside Mika and mention he could drink his to avoid any troubling feelings Mika may have about drinking blood. He 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 attacked. Inside at viewing the bodies of their deceased orphanage family members Yu was comforted by Mika holding his hand.

Akane Hyakuya

As children, Yu denied the statement when Akane said that they are all apart of the same family.[20] When she died, Yu was very saddened over her death.[10] He was completely enraged and even started to go berserk with his demon once Ferid showed him her decapitated head in a jar.[21] 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.[22] Once given to him, he then apologized to her for never calling her "family" and running away.[23] At Guren's mansion, he says that once he brings back Akane and the other children he will tell Akane they are family.[24] That Akane would be brought back is a significant reason why Yu is comfortable with human resurrection regardless of the cost.

Hyakuya Orphanage Family

Whilst he was not interested in the very concept of family at first Yu would become a paternal figure to the Hyakuya orphans as they lived 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.

Hyakuya Sect

Mahiru Hīragi

As a child Yu is visited by Mahiru while he is imprisoned and asked about the meaning of life. Yu at first tells her to go away, but she does not. When Yu explains to her that he is a demon spawn, Mahiru questions why he thinks that, and says he appeared human to her. Before the researchers mess with his memories, Yu is told to stay strong and that one day, she will return to free him from the Hyakuya Sect.[25] Eight years later, after Asuramaru finds this memory deep in his mind, Yu tells Guren that he vaguely remembers her but not her identity.[26] He would sees Mahiru's spirit once she separated from Noya and would remember who she was.

Saitō

He is saved by Saitō from his burning apartment and 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.

Japanese Imperial Demon Army

Shinoa Squad

Shinoa Hīragi

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In class Yu finds her as his appointed army surveillance officer.[27] She becomes Yu's first female friend in the army, and he joins her squad later on.[28] Yu eventually gets used to her teasing. After the battle in Shinjuku, Shinoa starts to develop a crush on Yu,[29] but he has yet to realize her feelings. He is able to convince her to help him save Mika, and they hold hands.[30] Yu shows guilt once he learns that he nearly killed Shinoa during his transformation at Shinjuku.[31] He saves Shinoa before Kureto murders her at Nagoya Airport.[32] Shikama Doji later reveals to Yu that she is in love with him[33] and tries to save her from his grasp, ignoring Asuramaru's warning.[34] He is devastated after seeing her in a comatose state to the point of ignoring his status as a former soldier and offering to be experimented on by Kureto's order, as long as Shinoa is saved.[35]

Yoichi Saotome

Finding Yoichi being bullied Yu would intervene and help him. He discouraged Yoichi from joining the Moon Demon Company due to his gentle nature. 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. When Yoichi was overcome by his demon with his mind lost Yu was adamantly against dispatching him. Yu threw down his weapon and appealed to Yoichi within to return and refused to inflict harm upon him. Later, they both are admitted to a squad under Shinoa. Like all his other comrades, he treats his friend nicely and is committed to helping him. Yu would be surprised at the swift advancement Yoichi makes with his cursed gear capabilities.

Shihō Kimizuki

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Yu crashes into Kimizuki (literally) on his first day of class for the Moon Demon Company. The two fight often at first and develop a rivalry, but they both have strong family values. He is a tidy person, who is good at cooking. He is a surprisingly caring individual. Yu considers Kimizuki as a comrade who he'd protect and a family member of their group.

Mitsuba Sangū

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When she first meets Yūichirō and her new group, she dislikes the idea of working with newbies and working under Shinoa, but she opens up and accepts them as time goes on. She and Yu mutually trust each other, and Yu does not mock her when she gets a promotion despite doing nothing on the battlefield. He says she can use her new authority to help him get Mika. Like the other members of his squad, Yu thinks of her as family. He is not aware of her feelings for him. 

Guren Squad

Guren Ichinose

Yūichirō meets Guren when he reaches the outside world. Guren rescues him because he knows Yu is a survivor of the Hyakuya orphanage, and he wants to use Yu to reach his goals. After that, he becomes almost like a father to Yūichirō and teaches him how to survive in that world and use a sword. Even after learning that Guren is experimenting on him, Yu remains loyal to Guren. Yu convinces Guren to help him save Mika. When Crowley captures Guren, Yu gets angry and disobeys orders to save him from the vampire. He acquired his whereabouts through Mahiru connection with Saito at the Hyakuya Sect.

Sayuri Hanayori

One of Guren's Squad members, Yu is taught by her in class.

Shigure Yukimi

One of Guren's Squad members.

Norito Goshi

One of Guren's Squad members.

Mito Jūjō

One of Guren's Squad members.

Shinya Hīragi

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One of Guren's squad members. He is made to battle him when Kureto suspects a traitor amongst them. He assists them in killing Lucal Wesker. Later on, he helps them escape Nagoya. A sniper.

Narumi Squad

Makoto Narumi

When Yu first meets Narumi, it isn't on good terms. After the Shinoa squad got in trouble, Guren assigned the Narumi squad to work with the newbies. Yu doesn't like the idea of someone who is older than him bossing his squad around. They are very argumentive at first, but they eventually grow on each other and see each other as someone to protect. 

Shūsaku Iwasaki

One of Makoto Narumi's squad members who died against the humans in Nagoya.

Rika Inoue

One of Makoto Narumi's squad members who died against the humans in Nagoya.

Tarō Kagiyama

One of Makoto Narumi's squad members who died against the vampires in Nagoya.

Yayoi Endō

One of Makoto Narumi's squad members who died against the vampires in Nagoya.

Others

Kureto Hīragi

The acting leader of the army and one of those involved with killing everyone in Nagoya. After learning he is the 2nd Trumpet The King of Salt he orders his soldiers to capture him. Yu offered his memories for Kureto and those under him for study to save Shinoa when she was being possessed by the first.

Aoi Sangū

Kureto Hiragi's aide. She is involved with killing everyone in Nagoya. He gives an impassioned defence of Mitsuba to her elder sister when they meet again.

Vampires

Ferid Bathory

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On their first meeting, Ferid asks for Yu, along with Mika to give him blood, but only Mika gives in. They meet for the second time when Yu and his family attempt to escape, and Ferid waits for them at the exit. Ferid slaughters their family in front of them. Although Yu managed to shoot Ferid in the head thanks to Mika's sacrifice, the injury is minor for a vampire. He believed Ferid was the one who turned Mika into a vampire. He has the gun Mika stole from Ferid prior to their escape attempt. Ferid is easily the vampire he resents the most for his massacre of his family-like friends, as shown by how he is the only Vampire Yu remembers and when they meet, he gets agitated and ferociously attacks him.

Chess Belle

One of Crowley Eusford's aides who he battles in Nagoya.

Crowley Eusford

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Upon the team's arrival to the gates of Shinjuku, Yu instantly recognizes Crowley as a vampire noble. The squad namely Yu manages to inflict some damage on Crowley, earning his interest. Yu is angered by their difference in power despite having a Black Demon weapon. Onwards at Nagoya's City Hall, when he learns that the vampire inside is Crowley, Yu fully agrees with Guren on the noble's strength.

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. He is surprised to hear that Crowley too was once human and heads into Ferid's manor with him before Yu attacks Crowley with a sword in a test of power. He is laid-back and pities the children for getting involved in Ferid's schemes.

"That's enough, Crowley Eusford! We aren't going to fight you!""
—From being wary before Yu now ceases to fight (Chapter 46 "Return of the Hero")

Horn Skuld

One of Crowley Eusford's aides who Yu would fight on more than one occasion.

Krul Tepes

Yu didn't meet Krul Tepes, however Mika explains him that Krul is the one who saved his life and she can be trusted, Yu shows sympathy about Krul since she gave Mika a second chance on living. She later discovers that her brother Ashera is in Yu cursed gear after sensing him. At meeting her Yu immediately classes her a friend and someone who they can trust and they escaped Shibuya together.

Lucal Wesker

The first noble vampire Shinoa Squad kills. They work in tandem with Narumi Squad and Shinya Hiragi where Yu leads the attack against the fifteenth progenitor.

Demons

Asuramaru

Asuramaru is a former vampire, who became a demon, and was cursed into a sword. He was Mahiru Hiragi's former weapon, and following her death, he becomes Yu's cursed gear after he makes a contract with him. Until Yu weakens the curse binding, Asuramaru promises to become his friend. Asuramaru gives him nightmares every night. He waits for an opportunity to take over Yu's body. After the battle in Nagoya, Yu is chained to a wall, and appears with fangs and horns with the wish of getting free. Asuramaru seems to have complete control over Yu's body.

When Yu tries to talk about Asuramaru memories he notes that every time his angel is out of control and his body and heart gets destroyed, he starts regaining little by little his memories, he says he has a feeling that he have a sister whom he regrets abandoning and falls asleep from the headache by remembering. After the Hyakuya Sect captures Yu, in his mind he's has been struck by two long spears weapons, while Asuramaru in front of him he suddenly finds it odd for his memories to be returning.

During the Dark Ages of Greece, when Ashera was a human, Sika Madu brought a slave named Yu to free the imprisoned Ashera. He tried to befriend Ashera, such as promoting him playing with him. However, Ashera was not interested but promised him that he will play with him someday if he got used to his situation. Ashera was not aware that Yu possessed seraph powers at that time, as the latter was astonished when he saw angel wings appear behind his back.

Shikama Dōji

Shikama Doji seems to be familiar with Yu, as after seeing him in Asuramaru's mind Shikama Doji tells him its been a long time since he last saw him. Prior to becoming the demon Shikama Doji, Sika Madu buys a slave named Yu with him to free the imprisoned Ashera and later tries to befriend Ashera, he used to obey every Sika Madu orders, having been with him for a long time likewise Sika Madu is fond of Yu and shows interest in him for unknown reasons. It is later revealed that Sika Madu only uses Yu such as the case when he used Yu's blood to turn Ashera into a vampire. He has no qualms of discarding him if he deems useless but Sika Madu kept Yu due to his blood compatible with Ashera which he takes interest in.

Later on Shikama Doji invades Asuramaru's heart and Yu comes to the rescue. Seeing both Asuramaru and Yu are in good terms he is delighted he also tempts Yu about his past as he known him for a very long time despite Yu's denial. He defeats Shikama Doji seemingly. telling Yu that he was just supposed to be another empty vessel. Yu wonders who he is as he knew his past.

Noya Hienma

Back in the Dark Ages of Greece, Noya seemed to know quite a lot about him. Though appeared cautious as the young Yu approaches the corpse of "Mikaela", taking interest in it, Noya tells him he could call it a fun toy. Noya helped young Yu see what is in the coffin before killing him. Noya did this believing it would save him, Ashera, and Krul and it's not a problem as Sika Madu will create more Yu's anyway. In the present, upon seeing a fully grown Yu, Noya is surprised.

Other

Mirai Kimizuki

Shiho Kimizuki's sister and an awakened Seraph of the End. He fights her in his seraph form and wins. He later resolves to help rescue her.

6th Trumpet

An Angel whom Yu fights and wishes to save him despite the 6th Trumpet have no desire to listen to him. Yu keeps fighting him together with Asuramaru whom he discovers he also has a demon inside. Eventually Yu and Kimizuki were able to stop him by pinning him down and inject him with a drug and now appears as a human. This also this puts an end to the Horsemen of the Apocalypse.

References

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