Yūichirō Hyakuya

"I... I don't care what people call me. Call me a demon. Call me a monster. Whatever. It's just... If I can keep my family safe... If I can protect the people who took in someone like me, I'll be happy... Everyone here is my family."

- Yūichirō to his squad

Yūichirō Hyakuya (百夜 優一郎), birth name Yūichirō Amane (天音 優一郎), is the main protagonist of the Seraph of the End: Vampire Reign series. He is a member of the Japanese Imperial Demon Army as well as Shinoa Hīragi's squad in the Moon Demon Company. He, along with Mikaela Hyakuya and a few others, possesses the "seraph" gene, which is relevant to the forbidden taboo and the focal point of the story, "Seraph of the End."

He also appears in prequel materials Seraph of the End: Guren Ichinose: Catastrophe at Sixteen and Seraph of the End: The Story of Vampire Michaela.

NOTE: "Yu" (one "u") is spelled as "Yuu" (two "u"s) when he first appears in the Catastrophe LNs, but this becomes "Yu" later on and matches the manga. His first name is always spelled "Yuichiro" with only one "u." Therefore, we will spell his nickname as "Yu" here.

Human
Yūichirō has medium length black hair which can be considered quite neat and messy at the same time. He possesses sharp green eyes which fall under his thick eyebrows. His eyes are large compared to most other male characters in the series.

As livestock, he wears the standard white uniform with short sleeves and a hood.

In chapter 2 of Vampire Reign when he is sent to school for his behavior, he is shown wearing his school uniform, gakuran with a standing collar that is black with teal trim. The collar and the top buttons of the jacket are unbuttoned, revealing is a white shirt underneath. He wielded a standard demon katana until he is promoted into the Moon Demon Company.

As a private of the Demon Army, he wears the standard JIDA uniform which consists of a long-sleeved black coat with light green details including the shoulder epaulettes which has a brown Sam Browne belt passing diagonally over his right shoulder and two rows of gold buttons on the front. Along with that, he wears a pair of white gloves and a white web belt with a gold waist-plate. He also wears the uniform trousers and black boots which go over the trouser's leggings. Yu keeps his katana on the left side of his hip. Sometimes he can be seen wearing the JIDA hat, and often wears the JIDA cape as well.

Demon
Yu's eyes become scarlet, sprouts two black horns from his head, and his teeth become pointed while curse marks appear on the side of his face.

Seraph of the End
In his incomplete seraph form, Yu's left eye turns dark and bleeds while a massive wing-like structure sprouts from his upper left shoulder. As a full seraph, Yu has a single pair of irregular black wings as a result of Asuramaru trying to prevent the transformations, both of his sclerae are dark with gold irises, and the edges of his hair become white.
 * Anime: In his incomplete seraph form, the transformation is more extensive. Yu's left eye eventually turns into a black pit, and his right eye becomes red. Then in his full seraph form, Yu's wings are brown cord-like limbs and the edges of his hair do not become white.

Human
Up until his teen years, Yu started off as moody and antisocial due to the tragedies in his life. As a young child, he saw himself as a demon that no one would love, yet he still held out hope of finding something good in this world. At first, Yu wanted nothing to do with Mika and the other Hyakuya orphans and even challenged Mika to a fight.

Shortly after though, when Mika puts Yu in charge of watching over the kids alongside him and Akane, Yu took on the role of the aloof, yet kindhearted older brother. After losing them, Yu reverted back to being a moody antisocial rebel with a thirst for revenge against the vampires that killed his family for another four years.

Eventually, when Yu opens himself up and becomes a hot-blooded youth with a kind heart. This becomes apparent when his fearless but somewhat reckless actions are shown when he is attacked by a Horseman, ignoring orders. It's made clear that this wasn't the first time. Yu is often called an idiot by those who know him. He is a very narrow-minded person, whose only goal is to annihilate all vampires because of what they did to his "family." He swore to exterminate all vampires for killing his family, especially Mika. Yu will take on any type of challenge in order to accomplish his goal.

Despite this, he has a soft spot, worrying more about his friends first than his goals. (Ferid Bathory considers this attitude to be "cute"). As a result, Yu empathizes with others who put their family first, as seen when a civilian girl gave his squad false information because vampires are holding her family hostage. After learning why she deceived them, he tells the girl that she did the right thing to save her family. He feels guilty for abandoning Mika and has nightmares about Mika's death for four years until he makes friends with Shinoa and Yoichi. After learning Mika is alive, Yu's personality changes in response and he grows more mature, as noted by Shinoa. He puts more effort into being patient and calm and making friends, and immediately amends his worldview to include Mika even though he is a vampire. His dream of wiping out vampires takes second place to reclaim Mika. Regardless, even though his best friend is now a vampire, Yu still slaughters them without mercy or hesitation. After Shinjuku, he becomes closer to his squad members and makes Guren promise to help him take Mika back under the promise that Mika will be useful to him, as he comes from the same orphanage as Yu. Additionally, friendship and bonds become more important to him, as shown in a mental battle against Asuramaru, to gain more power or else lose his body, he calls Asuramaru his friend and convinces Asuramaru to yield to him.

Rather than revenge, his primary goal changes to protecting his new "family," in order to avoid a repeat of past events. In Nagoya, he surprises Narumi's squad by memorizing all of their names and promising to protect them.

Similarly to how vampires do not bother to remember human faces and only think of them as "humans" or "livestock," Yu only sees vampires as "vampires" or "bloodsuckers" without bothering to remember their names or faces. He does not even recall the name of his vampire target in Nagoya. The only exception to this rule is Mikaela Hyakuya, who he still greatly cares for, and as Ferid Bathory was the one who murdered his fellow orphanages, Yu still cleanly remembers his resentment at Ferid and has been seen to rage when they meet again.

Aside from this, Yu shows to have a somewhat weird sense of humor, as shown when he teased Shinoa for her height.

1,000 years ago he was in good terms with Ashera Tepes and been with Sika Madu for a long time even obeying his orders, despite being used by Sika Madu all along.

In the Dark Ages of Greece, he express curiosity over minor or major things such as wanting to see the "Mikaela" corpse, even when very young his personality is similarity to the present one. According to Noya, that even one or more Yu's is killed, Sika Madu would just create dozens of him, upon witnessing the current Yu in the present time Noya is surprised to see a fully grown Yu, wondering if Sika Madu succeeded in finishing the human creations.

Seraph of the End
During his first transformation, he goes berserk and attempts to kill any human nearby. He displays no interest in vampires and recognizes no one. He also mutters that sinners must die, and he must kill all sinners.

Upon his second transformation, he curses the tainted humans and plans to turn them into "pillars of salt."

Namanari
In Yu's demon form, he acts like a standard demon. He wants to kill and destroy anyone nearby and screams and rages about being restrained. He even attempts to trick Mika with his blood and promises to run away with him if only Mika will set him free.

Thanks to Shinoa and Mitsuba's restraints, he has been unable to act on his desires.

When he returns to human form, he does not recall any of his actions as a demon. Despite this, he appears utterly nonplussed about losing his humanity, much to Mika's distress.

Until he receives medication for keeping the demon side restrained, he acts colder about everything, and Asuramaru notes he is able to think much more rationally without all of those emotions in the way. After receiving the medication, his personality returns to how it was before he became a namanari.

Dark Ages
In the dark ages, Yūichirō accompanied Sika Madu in buying Ashera from imprisonment and obeys his master's order in freeing Ashera. When Ashera asks if he is a bought child too, Yu just stares at him silently. He does not know and asks Ashera if he himself was brought, Yu does not remember anything. Yu asks who he calls Sigama whether he was brought but concludes that Sika Madu does not know either, but contemplates that it is possible he was before following Sika Madu.

When Sika Madu asks Ashera if he is hungry, Yu interupts that he is really hungry. He answers Sika Madu that whilst he ate not too long ago, enough to feel like he would pop he is hungry again, and asks why is that. Replying to Sika Madu, Yu asks what a growth spurt is and whether it means he will get to be big like him before abruptly stating that he is really hungry once more. He then cannot talk over his eating. A bowl breaks as Yu collapses to the ground as he shares that his tummy hurts, he is going to pop. He ate too much but asks if Sika Madu thinks if he has gotten bigger, or smaller when he is told overeating may be bad for ones health, Yu cannot eat another bite. Walking through the streets Yu asks Ashera how he knows his name when he speaks to him. Pointing to himself and waiting expectantly, Yu imitates Ashera awaiting for him to asks how Yu knows his name so that he could copy Ashera in saying that Yu heard Siga Madu call him that. Yu then asks whether he is amazing for being able to tell Ashera's name, in the same manner as Ashera learnt his name, from Sika Madu.

As they continue walking, Yu asks what Ashera means when asked about his duties. With the question simplified to what he does between waking up an sleeping, Yu answers that he eats, reads when Sika Madu tells him to then plays, eats again then sleeps when he is tired. Yu guesses it is the case that he plays all day when Ashera points it out to him. As to whether Yu is a slave he wants to know what one is, he also does not know if master buys child slaves a lot. One question Yu can answer after clarification is that Sika Madu does summon him to his chambers, just sometimes though. Back at Sika Madu's manor Yu takes a toy snake from a box and asks whether Ashera is going to play. In the face of Ashera's reluctance Yu insists that it is a lot of fun, adding sound effects to the snake. He is delighted when Ashera says he will play that with him remaining oblivious to Ashera's concerns on his survival chances.

By night time Yu stands by himself in Sika Madu's room. He is staring out the window when Ashera finds him at which point Yu holds his own face and yells as six seraph wings emerge from his back. In this state he expresses a seething hatred for humans for dabbling in the taboo and wishes to kill them. His eyes have changed and he glares at Ashera before being told to calm himself by Sika Madu. Hearing that an adjustment had been made on him so that he could stop does not prevent Yu from leaping into the air towards Ashera before being grabbed at the neck by Sika Madu. Feathers fall off him as he demands to be let go, he must kill all humans. Yu's rage intensifies and results in him using his right hand to cut his left arm clean off. He is able to break through the door where repeating his murderous intent he stabs into Ashera's chest. With this done he shouts and flies out of Sika Madu's manor towards the moon still holding Ashera. Hovering in the sky, Yu says the world is full to brimming with filthy, unrepentant humans and he must kill them. His murderous denouncements come to an end as Yu is unexpectedly decapitated by Sika Madu behind him and he falls to the ground below. With Yu's blood having accidentally got into Ashera, Yu's head is picked up by Sika Madu and his blood is allowed to drip into Ashera's mouth.

He is found sat on a throne in a large room container multiple containers each with a single black substance within. Yu's head is reattached but he remains unresponsive to Ashera, Sika Madu and the black matter above him that sinks extensions of itself into his head.

21st century
Yūichirō Amane was born on October 16, 2004. During his childhood, both of his parents screamed that he was a demon spawn. Yu's father tried to kill him, claiming that he had to kill the seraph of the end now or else the world would be ruined. His mother also goes mad and tries to burn their apartment down with Yu inside, but he is saved by Saitō of the Brotherhood of a Thousand Nights. His mother screams about killing the demon before she sets herself on fire, burning herself to death and committing suicide.

The Hyakuya Sect then used Yu in experiments and later erased his memory of them. On the day of the Apocalypse, Saito brings Yu to one of the orphanages and leaves him in Mika's care.

Events of 2012
At 6 p.m., the news shows a fire at an apartment complex. A disheveled woman in her mid-twenties with long, silky black hair then steps out of the crowd and screams for Yūichirō. She screams about a demon and says the fire should never be put out, and says the demon child should be killed immediately. She then lights herself on fire which causes firefighters to tackle her.

Saitō from the Thousand Nights appears and approaches the camera before the footage is cut.

Days later, Mahiru visits Yu, who is being experimented on and abused by the Hyakuya Sect. She asks him about his reason to live and if he has no right to live if he is a demon. Yu does not know how to answer. Since his mind has not broken from his experiences, she tells him he will find an answer one day. A researcher says he will erase all memory of this conversation from Yu’s mind.

Near Christmas, Yu is being driven by Saitō. He tries to get the man to answer where they are going, and Saitō eventually tells Yu that he is evacuating him to the Hyakuya Orphanage far from Shibuya. When Saitō brings up with the prospect of Yu getting along with the kids like him, Yu shoots it down as he believes his parents' claim of him being a demon child, hence no one would care about him. Saitō doesn't believe it, but Yu brings up his (not) mother's death, and it brings tears to his eyes. Saitō tries to encourage Yu to smile, but Yu refuses and turns away to look out the window. He ignores Saitō's comments, and even the option for him to die by jumping out of the speeding car, which the boy remained sitting with only his shoulder quivering a little.

Yu then tells Saitō that he will not die because there is something good in this world which the man doesn't believe, so the boy explains about the scientists talking about him meeting someone and being blessed by something. Though when Saitō brings up Yu making friends at the Hyakuya Orphange, the boy continues to believe there won't be any friends over there.

Prologue
When Yu arrives at the orphanage, he meets Mikaela and the other orphans. Seeing as the two 8-year-olds were the eldest, Mika wanted them to be friends, but Yu rejected him. Mika asked if Yu was challenging him to a fight and said he was the leader. They fought, and Mika gave him a serious smack-down.

Afterwards, he told Yu that he used to be alone like him, but now he had a big family. And from that day onward, Yu had one too. Yu told him about his parents' violent behavior, saying that "family" no longer meant anything to him. Mika smiled, saying that both of his parents abused him until they got sick of him and threw him out of a moving car. The orphanage took him in after that. The other children shouted out their stories, saying that they never met their parents, their parents committed suicide, or their parents left them at the orphanage door. Mika then told Yu that they weren't lonely because that day was the day their new big brother Yu joined them. Shortly after, the director suddenly began to bleed from her nose and mouth and collapsed to the ground.

The adults perished, and Third Progenitor Krul Tepes led the vampire invasion on Tokyo. For the next four years, the orphans survived as livestock for the vampires in the vampire capital of Sanguinem, which is located under Kyoto.

Events of 2016
In Sanguinem in 2016, Mika donates his blood, cringing as the needle pierces his neck. He chats with Yu, who is sitting next to him. Mika thinks Yu is kind because he always maintains the children's hope about defeating vampires.

Once they finish up and leave, Yu asks him what is wrong and says Mika is spacing out. Mika only says he feels tired after donating blood. Yu prattles on about killing vampires again before telling Mika to not carry everything on his own shoulders. Mika knows that one wrong move will get him killed, and he cannot risk Yu dying.

Mika tells him not to worry and asks what Yu's surname is, but Yu cannot remember. Yu asks Mika about his family since he does not look Japanese. Mika's mother was Japanese but his father was Russian. Mika says his last name was Shindō. Mika says all of the orphans use the surname Hyakuya because they are all family.

Mika sees Ferid Bathory's mansion and splits off from Yu.

Prologue
In the current time, Yu tells Mika about how to kill vampires based on a book he's reading, from crushing their heads to removing their armband devices, while the two were giving their blood. Afterward, Yu rants to Mika that he is tired of always giving their blood and how the vampires viewing them as "livestock". The two then are approached by Ferid Bathory, whom Mika greets. He invites them to his house to partake of their blood, but Mika agrees to go while declining politely for Yu, claiming Yu to be "shy". When Yu asks Mika about his meetings with Ferid illicitly, Mika explains how Ferid's nobility status grants him access to entitlements. Angered at this news, Yu hits Mika on the head in disapproval before leaving him. Later in the day, Yu was lying on the ground still fuming about Mika when Akane comes by. When she asks about Mika, Yu refuses to talk about him and tells her to go away when asked why he is upset. Akane reminds Yu that he is part of the same family which the latter denies. The two reminisced about Yu arriving at the Hyakuya Orphanage and the start of the Apocalypse four years ago that led them to Sanguinem. Akane then tells Yu that everyone is waiting for him to have dinner before leaving.

When Yu comes home, he becomes frustrated when he learns how Mika was able to get his family enough fresh ingredients to make curry. When Mika arrived later that night, Yu tells him that the children loved the curry and asks what he had to do to get the ingredients. Yu then offers to donate his blood which Mika rejects and scolds him. Yu then becomes concerned when Mika briefly breaks into tears when telling the former that his dedication to slay the vampires keeps the children's hopes up. He then shows Yu a map of the underground and a gun so they can make a daring escape with their orphanage family.

They are able to get to their family to the city entrance which turns out to be a trap set by Ferid. The vampire noble then proceeded to slaughter the other children in front of Yu and Mika. Yu manages to shoot Ferid in the head, but Mika was fatally wounded. Yu calls Mika "family" for the first time. He refuses to leave Mika behind until Mika yells at Yu to leave and pushes him away. Yu escapes, leaving Mika behind; an action that would haunt him for years afterward. After reaching the outside world and realizing the vampires lied about the world's destruction, Guren Ichinose of the Japanese Imperial Demon Army found him.

Guren mentioned a prophecy and knew that Yu was one of the lab rats from the Hyakuya laboratories. He was one of the children that were being experimented on by the Hyakuya Church to create a weapon of mass destruction, as part of the 'Seraph of the End' plan in destroying the world. Guren knew of this beforehand, thanks to intel provided by Mahiru in 2011. In order to take revenge for his family, Yu joins the Japanese Imperial Demon Army as Yūichirō Hyakuya.

Second Shibuya High Arc
Four years later, Yu is a foot soldier to the Japanese Imperial Demon Army. He continues to be haunted by the death of his family and was recalling that gruesome scene while standing in the middle of Shibuya's streets when he is ambushed by a Horseman of the Apocalypse. Two more soldiers appear in front of Yu and command him to run, but Yu proclaims that his only life purpose is to exact revenge on the vampires before he easily kills this monster in one slice. For this act and his repeated insubordination acts, Yu gets suspended from the army and forced to attend Second Shibuya High in the meantime.

During class, he annoys the teacher with his mumbling and gets threatened with the suspension which Yu's reacts with cheer. He is then tapped by a girl sitting behind him, who uses her notebook to introduce herself as Shinoa Hīragi, his appointed surveillance officer, and tells him to cooperate or she will prolong his suspension. She also mentions that his punishment will end once Yu makes a friend.

Yu recalls his first meeting with Guren, who promised to give him the power to take revenge on the vampires. Now four years later, and Yu wonders why Guren is not letting him kill any vampires yet. Yu stays at his desk as the class ends while everyone else leaves. Shinoa stays behind and tries to encourage Yu to start making friends, despite it being a struggle for him since Yu has stubbornly rejected forming close relationships since Ferid Bathory slaughtered his family. He insists he does not need any friends, but Shinoa gives him a note from Guren specifically written with the orders to make a friend; he promptly wads it up and throws it to the floor. With a little persuasion from Shinoa, he steps in to save Yoichi Saotome from bullies. Unfortunately, Shinoa tells him his punishment will be extended if he harms any civilians which leads one of them punching Yu.

Later on, Yu is outside walking with Yoichi and Shinoa while carrying drinks for Yoichi. He learns from Yoichi that he failed the admission test to get into the Moon Demon Company, and tried to become friends with one of the bullies named Yamanaka, a soldier in the Moon Demon Company, to retake the test. Yu becomes angry at Guren and rants at Shinoa upon learning this, and Yoichi says he wants to join the army to get revenge for his sister's death, but Yu tells him to forget the army as his sister wouldn't want him to avenge her death, and the army would not accept somebody as weak as him; which nearly makes Yoichi cry.

A building suddenly explodes from behind them followed by an emergency warning that a vampire has escaped and is close to the school. Yu decides to go after it to prove himself to Guren, so he first rushes to his locker to grab his sword and gun, and soon finds the vampire in one of the classrooms, which Yamanaka is also in. Yu's approach interrupts her feeding and the two fight. While the vampire is on the opposite side of the room, Yu asks Yamanaka to save the girl on the desk since he is an army candidate, but Yamanaka reveals it was a lie. The vampire then continues the fight with a metal pole in her hand which Yu gets rid of. He tries to shot her with his gun, but she easily avoids his attacks and ends up back with the unconscious girl. Yoichi is able to stop her feeding by tackling her to the ground, and Yu protects him by intercepting the vampire's strike. The vampire then grabs Yu by the neck and pushing them through a window. They fall to the ground with the vampire still holding Yu's neck while Yu has his blade stabbed through her. Guren then arrives and ends her life.

Yu claims he would have been able to kill her, which Guren says he won't accept those that do not understand teamwork. Yoichi then arrives and hugs Yu, but Yu ends up passing out. Since Yoichi considers Yu a friend, Yu has reached the requirement Guren gave him. In a dream, Yu's orphanage family tells him farewell. Yu wakes up, and learns from Shinoa that he and Yoichi have been accepted into the Moon Demon Company. The next day, Yu is given a letter which is from the girl he saved from the vampire. Shinoa then turns up and teases him to start building a relationship so humans can get their population back up to survive. Yu then asks why he is still stuck in Second Shibuya even though he is in the Moon Demon Company which Shinoa explains by showing him her Cursed Gear, Shikama Dōji. Yu tries to take it from her by force, but she quickly relieves him of that notion by manifesting her demon to slam Yu into the fence.

Yoichi then runs up to them with Yamanaka and his friend chasing him. The two reveal that they want to become Yoichi's disciples, and they begin praising Yu upon seeing him. Yu asks them if they have any pride for begging help to people they used to bully, which Yamaka explains that they want their help in saving their friend, Yūji, who went into the Forbidden Chamber and failed to return. Yu, Yoichi, and Shinoa decide to go into the Forbidden Chamber to rescue Yūji, but upon reaching the restricted area, Yu rushes in and fights Yūji for the battle-ax in his hand. During the fight, Yu makes contact with the myo-o demon but breaks out of the demon's illusion on his own, surprising Shinoa. She agrees to notify Guren.

Later, Yu meets and fights with Shihō Kimizuki before attending his first class in the Moon Demon Company Barracks. Guren introduces Yu as the idiot and Yoichi as the crybaby. Yu gets paired with Kimizuki for a practice test. When Kimizuki's sister goes into critical condition, Yu punches Kimizuki and convinces him to go see her during the middle of the exam. They become friends and rivals. Shinoa recommends both of them for the Black Demon Series.

Although Yu earns a zero on his spellcraft exam, which is supposed to help determine what rank of cursed gear he can receive, Yu is permitted to try for a Black Demon Series weapon along with Yoichi and Kimizuki. He appears to be nearly illiterate since he used no Kanji on his exam and wrote everything phonetically. Yu challenges Asuramaru, earning the demon's power in order to protect everyone, and Asuramaru informs Yu that 1/10th of him is not human. Afterward, Yu talks to a possessed Yoichi and helps him to regain control over his demon Gekkouin.

Shinjuku Arc
On his first day in the army, Yu meets Mitsuba Sangū, who completes their 5-person squad. A Horseman of the Apocalypse chases a young girl. Against Shinoa and Mitsuba's orders, Yu rescues the girl, and a group of vampires attacks him. Mitsuba slaps him for his disobedience, but he declares he does not regret his decision.

They then use information from the girl to lead an attack against the vampires. Although the vampires seize Mitsuba, Yu's strength shines through, and he rescues her. Even though the girl deceived them, informing the squad that there were only seven vampires instead of nine vampires, Yu tells her she did the right thing to protect her family. Her father, however, shouts at the group, telling them that they now have nowhere to go beyond the slums, and that they will have to deal with the monsters on their own. Yu attempts to reason with him, explaining that when he was little, he had to deal with vampire persecution in Sanguinem, and that the day he decided to run away from it costed the lives of his entire family. He abandoned them to die so that he could live, and even though the guilt of that tears at him sometimes, he refuses to allow himself to regret it.

Before they head to Shinjuku, Kimizuki hot wires a hummer. This impresses Yu, who says he had not been in a car since he was little and anyone rarely uses cars in Shibuya since gas is such a precious commodity. Yu attempts to drive and nearly accidentally crashes into his squad members, leading Kimizuki to violently remove him from the vehicle. Kimizuki promises to teach him how to drive on another date. As they head to Shinjuku, they encounter Thirteenth Progenitor Crowley Eusford. Yu manages to take his right arm momentarily before Crowley is summoned away by Seventh Progenitor Ferid Bathory.

They reach the battlefield in Shinjuku, and Guren summons Shinoa's squad to the 5th Street intersection. After taking his supplement, Yu charges into battle. Enraged overseeing Guren getting stabbed, Yu pierces Mika through the chest with Asuramaru, calling him a bloodsucker and telling him to die. Then, he recognizes his not-quite-dead best friend and family member. Guren grasps Mika's sword with a spell tag and urges Yu to activate his weapon and kill the vampire, but Yu freezes when he realizes who he just stabbed. Mika releases his sword and escapes. Guren hits Yu and asks him why he did not kill that vampire when he had the chance. Yu says that person is Mika, his family. He cries from happiness. Ferid steps behind Yu and grabs his shoulder, causing Mika to amputate the responsible appendage. Of course, Ferid says he was just joking about tasting Yu. Mika steps up to Yu and tells him to forget about the humans and run away with him.

He lifts Yu and carries him in his arms. Mika warns Yu that Yu is in a bad place and is being used by humans, but Yu has no idea what he is talking about. Yu struggles and breaks free, jumping to the ground. He says that Mika makes it sound as though he is no longer human and asks if it is his fault. Mika immediately tells him it is not Yu's fault. Mika begs Yu to come with him, insisting that he is Yu's only true friend and the humans are only deceiving and using Yu. Yu looks back when Shinoa screams and sees his comrades defeated by the vampires. When he tries to help them, Mika grabs his wrists and says they have to go. Just then, the special supplement Shinoa gave Yu under Guren's orders takes effect, causing Yu to transform as his seraph component runs wild. Yu screams.

Yu swings at Mika and Crowley before moving to kill Shinoa, his true target. Mika jumps in the way, and Yu stabs him through the back. Mika urges Yu against killing humans. He asks Shinoa how she could dare use Yu like that, and the berserk Yu calls Mika a vampire, telling him to not interfere and saying that all humans must be killed. Guren orders Shinoa to embrace Yu to undo the transformation, so she jumps in after Yu flings Mika aside. Yu cries out and hacks up blood before passing out.

Post-Shinjuku Arc
Yu wakes up exhausted a week later. He wakes up a sleeping Yoichi who was sleeping at the end of his bed. He asks what happened, but Yoichi is overly-excited and rushes to inform the others first. Yoichi says that Yu was the only one who was badly injured and spent a week in a coma. Yu comes to realize that Mika is truly alive after all, and cries tears of joy, only for Shinoa to show up and tease him.

Yu does not remember anything after Mika asked Yu to run away with him. Shinoa tells Yu that he suddenly collapsed on the battlefield. She says that many non-noble vampires were killed, with a lot captured, but over half escaped. Yu asks about Mika, saying that he does not care if Mika were the enemy or an ally. Shinoa says that Mika refused to leave Yu's side until another vampire dragged him away. She advises him against any stupid rescue attempts, and Yu says that he is not that stupid and is happy enough knowing that Mika is alive.

The rest of Shinoa's squad arrives, and Yu apologizes for making them worry. He then says that he is glad everyone survived and is blessed with great friends. The squad asks him if something is wrong with his head, and then inform him that they are on leave until Yu is approved for battle again.

Later, in his hospital bed, Yu swears he will save Mika.

He looks up books on vampires to try and learn how to turn Mika back into a human. Later, Lieutenant General Kureto Hīragi summons Yu to the Shinjuku Central Army Headquarters First Office where Kureto sicks a starving unarmed vampire on him. Yu kills the vampire without hesitation. Kureto challenges him to a duel but cheats, winning quickly. He then attacks Kureto while his back is turned, but his aide intercepts. He also makes Major General Shinya Hīragi confront Yu. Kureto tortures Yoichi and Kimizuki to try and get information from Yu. He tells Yu about the Hyakuya Sect, asking if Yu was from that family. Yu knows nothing about them.

Guren tells Yu he knew about Yu's connection with the sect all this time, and he agrees to help Yu get Mika back. Shinoa and Mitsuba teach the squad about possession- and materialization-type demons. Yu weakens the curse binding his demon before Kimizuki and faces illusions of his orphanage family and his biological family. After Kimizuki conquers his demon as well, the two spar. Both of them use special abilities, which should be impossible for the possession-type demons they use. Yu uses a technique called "Asura-Kannon," ordering it to fan-out which produces numerous materialized swords.

Shinoa tells Yu about what he really did on the battlefield of Shinjuku, and they agree to side with Guren in the upcoming political power struggle.

Nagoya Arc
Yu hears screaming and goes down with Kimizuki and Yoichi behind him to find Mitsuba and Shinoa with a frying pan on fire. After Kimizuki steps in and cooks breakfast, the squad eats where Shinoa tells Yu about his transformation and going berserk in Shinjuku which brings into question whether they can trust Guren or not. She also brings up the power struggle that Guren will start against the Hīragi family for control in the Demon Army, yet Yu and everyone agrees to remain loyal to Guren.

The squad then depart for Nagoya with Kimizuki driving the squad down the Tomei Expressway, which is somewhere between Tokyo and Nagoya, dodging Horsemen that are on the road. Yu leaps out to slay one or them, and a series of pranks ensue. At some point, Kimizuki lets Yu drive the rest of the way to the Ebina rest stop. Shinoa briefs them on their mission.

Yu wanders around the Ebina rest stop. He chats with Yoichi and Kimizuki until Sergeant Makoto Narumi and his squad arrives. The two squads are paired together for this mission. Narumi says he does not trust a bratty kid who showed up late to his first meeting. Yu asks Narumi his age, and he answers nineteen. In response, Yu says he is twenty with a baby face. Shigure summons Yu for his punishment, and Shinoa and Mitsuba attempt to take responsibility for the squad's tardiness. Yu meets with Guren's squad.

Guren is already aware that he is covering for his friends, and he appreciates Yu's development from being so focused on revenge to being loyal to his new family. Shinya and Goshi tease Guren, and Yu asks them if Guren considers his squad family.

Guren tells Yu is here to punish Shinoa. Goshi begins a humiliating illusion of a bound and naked Yu with four tiles piled on his thighs. Goshi makes the illusion Yu cry for forgiveness, help, and his mommy, screaming that he peed his pants. Shinoa's squad rushes in, and Shinoa quickly orders Shikama Dōji to destroy that illusion. Guren lectures Shinoa, scolding her that a little mistake could cost her family and squad their lives. He challenges her to a test: Guren, Mito Jūjō, and Shinya Hīragi in a fight against her entire squad. He gives her ten seconds to prepare. Shinoa assigns Yu and Kimizuki to keep Guren busy. She orders the squad to stay within the radius of her scythe. Kimizuki and Yu do not have time to explain their abilities. Yu and Guren clash. He manages to hold his own against Guren, impressing the other soldiers. Guren attaches an explosion charm to Yu's head, and Shinoa makes to disenchant it. Jujo stands on her scythe, disabling her movements. Yu charges Guren, and Shinya fires Byakkomaru at him. Guren takes the opening to slip past Yu and breach their lines. He tells Shinoa's squad that it is over, and all their friends are dead.

He introduces them to the other soldiers as 16-year-old rookies and states that three of them bear black demon weapons. Yu attempts to pick another fight with Narumi, and Mitsuba bashes him over the head. Shinoa apologizes for him. Shinoa's squad agrees that they desperately need to work on their teamwork, and the operation commences. The squads mobilize and head to Nagoya.

Within Lucal Wesker's ward in Nagoya, Narumi and Shinoa's squads have ten minutes left before beginning their assignment. Their target is Fifteenth Progenitor Lucal Wesker. Although Yu fails to recall their target's name correctly, he lists the name of every soldier on the two squads, promising to let none of them die. On the ground, Yu acts as a point for the squads and charges Lucal Wesker. Kimizuki, Shinoa, and Narumi jump in. Lucal swings Shinoa in Narumi's path, but Yu defends her. While Yu's back is bared, Lucal claims Yu is too powerful for a human and moves in to attack him. Mitsuba summons Tenjiryū's dummies to defend Yu, but Lucal banishes them with a wave of his hand. Kimizuki strikes, but Lucal disarms him. Rika manages to make the first successful attack against Lucal by stabbing him with her weapon from behind. Shusaku summons his demon Akahebi, which becomes a chain binding Lucal's left arm.

By cutting off his own arm, Lucal avoids Kimizuki, Yu, and Narumi's attacks against him. Kimizuki taunts the vampire, asking if a vampire can regrow his arm if it is vaporized with a curse. He tells Lucal to beg for it if he wants it back, sending the vampire into a rage. Lucal charges in, swatting away Shinoa and Mitsuba's attacks. Yoichi and Shinya fire at him. As he dodges, Yu strikes, slicing the vampire in half and Narumi finishes him. The two squads cheer.

On the streets of Nagoya, Shinoa Squad and Narumi Squad wait for the survivors to regroup. Sergeant Aiko Aihara arrives with a bruised, battered, and bleeding face. Kimizuki notes that Aiko's squad only has seven survivors, so eight of them died. Yu offers to have his squad take watch while hers rests, and she takes him up on it. Guren and his squad come above ground, but they are all worse for the wear. Narumi reports that Shinoa Squad did very well.

Guren orders Shinoa Squad and Narumi Squad to join his squad and hunt down Crowley, Chess, and Horn. Guren orders them to stage an attack on Crowley that will last ten minutes. If they cannot kill him during that time, they will retreat and tackle the next mission with those numbers. Guren orders Aiko to hold the position for thirty minutes and pass on orders to any late teams to report to Nagoya Airport. Anyone late is presumed dead. Once they reach Nagoya City Hall, Guren looks at the hostages being used through a telescope and knows that they are being used as bait to lure them. Yu insists on bursting in and saving them. Narumi dismisses it as too dangerous and when Yu asks him what they should do, Narumi asks Guren what they should do. Guren suggests that they snipe them from their position and see if they can lure them out but says that if there are too many of them, they are to abandon the hostages and run. Yu shouts that they can't do that.

Shinoa interrupts Yu and asks Guren what their priorities are. In order, he says that their top priority is to maintain their numbers, letting no one die. Their second priority is to free the hostages and lastly, getting the hostages out alive. Narumi states that this is because they are needed for another mission after this. Guren then says that they need to keep the vampires occupied in Aichi Prefecture for as long as they can so they can buy enough time for the main forces in Shibuya to get prepared.

After Crowley catches Gekkōin, Guren and his squad discuss what to do. After careful planning, Guren decides that his squad will take his squad to attack Crowley while Shinoa and Narumi Squads free the hostages. He gives them five minutes to rescue as many hostages as they can and act as a proper diversion for the main force in Shinjuku. As soon as the five minutes are up everyone has orders to retreat to the Nagoya Airport immediately.

Sometime later, Yoichi reports on the situation with Guren's squad to the squad and Yu insists on rescuing him. Shinoa agrees with him but says they only have five minutes. She gives them specific instructions regarding their plan. Yu breaks through the floor and attacks Crowley. Crowley blocks easily and moves to decapitate Yu. Kimizuki parries the attack, and Mitsuba distracts Crowley by summoning dummies with Tenjiryū. Yu uses Asura Kannon, but Chess and Horn immediately step in and defend Crowley from it. Chess and Horn counterattack and rip apart the shield Mitsuba forms with Tenjiryū.

Guren orders Shinoa Squad to leave. Crowley recognizes Yu as the one who went berserk in Shinjuku. When Yu moves to rescue Guren, who is on the ground behind Crowley, Shinya stops him and orders him to abandon Guren. Shinoa says their five minutes are up and orders a retreat.

Outside, Yu breaks free of Kimizuki's grasp and complains about leaving Guren behind. Yu asks if ignoring feelings and abandoning family is acceptable as long as it is for their mission. He holds back tears and states that would mean giving up on family. He calls Guren family.

Yu recalls four years ago after Guren picked him up from Sanguinem. One of Guren's men reported that Yu woke up screaming, and Guren comes to check up on him. Yu cries in his bed. Guren asks about what dream Yu had, and Yu says its the same one he always has: Ferid Bathory slaughtering his family. Guren asks if this means he wet the bed again, and Yu snaps, stating that he ever wet the bed. Guren says he will stay there until Yu falls asleep. He sits by Yu's bed and reads documents on the Seraph of the End project begun by the Hyakuya Sect. He stays there from 2:20 a.m. until 2:50 a.m. Yu says he has never really had a family since he was born because his parents called him demon spawn and tried to kill him. He says he made a new family, which was killed anyway. He says that living is painful and wants to know if it is even worth it.

Guren states that living hurts him, too. He says he failed to save the one he loved most, but, if he sticks around, then a day may come where someone needs him. He instructs Yu to live until he finds a new reason for life and people who need him. He leaves Yu and orders him to sleep.

In the present, Yu wipes away his tears and states he cannot follow orders. He says he is not cut out for teamwork. He tells the others to proceed without him, and he will stay behind. He says he would rather die than be unable to save his family. Before anyone can stop him, he swallows two curse stimulant pills for a total of three since the beginning of the mission. Shinoa orders him to spit them up, but Yu begins to cough blood. The curse power overwhelms him, forcing blood out of his eyes and making him scream. Yu coughs up blood after overdosing on pills to increase his power at the end of the previous chapter.

Inside his mind, Asuramaru, calling him hopeless, comments on how Yu appeared to give up on revenge and then became obsessed with living and family. Yu says he does need the power to save Guren when Asuramaru asks him if he wants the power that badly. He begs Asuramaru to give him power which the demon agrees to. If Yu wants power, he’ll give him all he asks for and more since he feeds on ugly human emotions like obsession and greed. However, he complains that the pills Yu took before are a problem as they force the curse to go crazy while keeping his greed in check. Asuramaru says that the contradiction won’t do. He states that Yu cannot expect to just take drugs and get stronger without any consequences so Yu asks how he can get stronger.Asuramaru says he can’t answer that as Yu is already dead. He says that it was a quick death. Yu took so much of the drug that all his internal organs ruptured and his heart exploded. He says while he has powerful regenerative abilities, but that kind of damage is beyond him. He says Yu’s done. Dead. Then, he amends his statement, saying that at least he should be. The only reason he isn’t is that of those disgusting angels. Their power is forcibly keeping him alive. They peer into the background of Yu's mind and see something lying on the ground.

Yu asks Asuramaru what it is, which the demon says he doesn’t know but from there it looks like a trumpet. Yu has the urge to take the trumpet, but Asuramaru warns him not to take it and insists that Yu take him instead since angels can be far nastier than demons.

Upon noticing that Yu’s heart has started beating again, Asuramaru says that now that it’s fixed, he can take care of the rest. He stabs into Yu's abdomen, telling him not to go with the trumpeters and instead stay with him, accept him. He tells Yu that he can heal him but when he tries to he says that he cannot return Yu to normal. He complains that Yu lost even more of his humanity than before and has become even uglier.

The demon orders him to never do that again and claims Yu's body is his. Yu says he does not care and demands for Asuramaru's power. Asuramaru calls him a greedy little human wretch and tells Yu that he has already given it to him as three pills worth of the drug is in effect. He can use all his strength for the next two to three minutes without becoming a demon. Yu wakes up to his friends' panicked faces. He says he is okay and has something to do. With immense speed and power, he leaps from the ground and breaks through the wall to reach Crowley and attacks him. He demands that Crowley give Guren back, and Crowley wonders if he is really human. The two fight and Crowley delights in the fact he may have to use both hands for once.

Guren, whose wrists have been bound, gets between them and orders Yu to leave. When Yu asks why he is still not strong enough, Crowley answers that it is because Yu is only livestock and asks if Yu fears cows and pigs revolting someday. He insists vampires will never fear humans. Yu repeatedly yells at him to shut up and die, and they exchange blows. Guren orders Yu to stop. He says that Yu's demon will take over if he uses more power than that. Yu refuses to leave.

Crowley mutters that he is beginning to get bored and decides to kill Yu. Guren tells Yu that he has a plan, but Yu needs to leave. Yu does not listen and demands even more power from Asuramaru.

Asuramaru is delighted to help, especially now that the protection from the drug has completely worn away. Yu's desires overwhelm him, and half of his face darkens and a horn sprouts from his head as he becomes a demon. Yu enjoys the power. Crowley says that Ferid always makes interesting things happen. He says that Yu is so lively and full of energy that he wants Yu's blood now and mentions he may drink Yu dry the next time he gets close.

Yu challenges Crowley again. He hears telling Kiseki-Ō to begin the count to nine until the devil's coffin opens. After Kiseki-Ō gets to four, Yu invites Kimizuki to kill this bloodsucker together, but Kimizuki notices Yu's horn. Guren warns Kimizuki that Yu has been possessed and to grab him and run. Yu tells Guren to shut up now that he has the power to rescue him.

Kimizuki tells Yu that what he said before was right. In this screwed up the world, there's no point to living if you don't have a family to cling to. He then says that's why it's his turn to rescue him. Kiseki-Ō finishes the countdown and captures Yu with the devil's coffin. Kimizuki joins with the rest of their squad while Kiseki-Ō begs to kill Yu, who is in his coffin. Kimizuki orders him to only knock out the demon inside of Yu. He orders Kiseki-Ō to spit him out and catches Yu in his arms. Yu remains unconscious throughout Mika's confrontation of Moon Demon Company and remains so when Mika flees with him.

In Yu's mind, Asuramaru approaches him. He says that he is really starting to like Yu and praises Yu's honesty about his desire. He says that Yu is broken and does not distinguish between good and evil when it comes to protecting his family. Yu asks Asuramaru about what happened which the demon says he only knows what he saw through Yu's eyes. He offers power to Yu, but he turns down his offer this time. Asuramaru says Yu's friends are weaklings who will only drag him down and weaken him again. Yu says everything will work out as long as he is with his friends. They argue, and Asuramaru says he will fail no matter how hard he tries. Yu says he is going to work with his friends to save Guren, but Asuramaru asks about the other family member who came to visit Yu today before waking up.

Yu finds himself in a ruined convenience store and hears panting at the other end of the isle and sees Mika. He calls out to him. Mika mutters about human blood and attacks him, not able to recognize Yu and throwing him to the ground. He calls Yu a human and tells him not to resist. He screams about he pain and begs for blood. Yu stares at him, confused, but tells Mika to drink his blood.

Mika jumps on top of him, pinning him to the ground. As Mika is about to bite him, Yu apologizes for having left him behind which causes Mika to snap out of his blood lust and quickly moves away from Yu.

Yu asks him about his thirst and says it's his fault for leaving Mika behind. Mika says he already told Yu it was not Yu's fault. Yu begins crawling toward Mika, but Mika tells him to stay back. He does not want to drink blood, but Yu wants to alleviate Mika's suffering. Mika says to not worry about it and says there is something he must tell Yu.

Yu grabs onto Mika and says he does not care. He says that Mika looks like he is about to die and asks if drinking blood will heal him. He offers his blood for a second time, pulling open his shirt collar. Mika tells him to stop, saying that Yu is making it difficult to resist. Yu focuses only on what he has to do to save Mika and says he does not want to watch Mika die again.

Mika says he has yet to drink human blood since he will not be able to turn back and will forever be an immortal and ageless vampire. Yu turns the words around and asks if drinking his blood means Mika will not die. Yu asks Mika for a favor, but Mika rejects him before Yu can even say what that favor is. They argue. Yu finds it acceptable to turn Mika into a true vampire, but Mika says he refuses to become a monster. Yu says that Mika should live for his sake, even if he has to crawl through the mud to do it.

Tired of this conversation, Mika says there is something he must tell him, but Yu responds by covering his ears and saying he cannot hear him. He says he will only listen if Mika drinks his blood first. Yu takes some broken glass and cuts open his wrist. He refuses to let Mika die. Mika calls him a jerk, and Yu says he is the one who took that cruel jerk and told him he was family. Mika calls him the worst and says it will be his fault for becoming a monster. Yu says that drinking a little blood is not enough to turn Mika into a monster. He says they are still family, no matter what Mika is. Mika begins crying.

Yu offers his blood for the third time, holding out his bleeding wrist. Mika tackles him in a hug and bites into his neck, and Yu welcomes Mika home.

After drinking, Mika apologizes. Yu says it did not hurt much. Then, Yu notices Mika's eyes change color. Mika blames Yu for turning him into a monster, so Yu tells him to growl or something then. Mika says surviving by drinking blood from his own family is not normal, and he is a failure as a human. Yu says he is fine if he is not normal. He says Guren took him in and told him to live, even if his only reason was for revenge. Guren said Yu might find someone who would need him again, and he found Mika.

Yu says he does not care if Mika is a vampire now, and he will find a way to change Mika back if Mika ever gets sick of it. He tells Mika to never try to go off and die again, and Mika states that he is the one who is supposed to save Yu. Yu says he is stronger than he used to be causing Mika to laugh.

Mika says Guren is probably just using Yu, but Yu says he does not care if either Guren or Mika want to use him. Mika sees this as too risky and says he will never use Yu. Yu points out that Mika just drank his blood. He says Mika may drink however much he needs in exchange for helping him rescue his new family. Mika warns him against the Demon Army and draws his sword against Yu when Yu insists on finding his family. Yu states he wants to rescue his family, and Mika is obligated to help him. He says he would rather die than be unable to save his family. Mika reveals that the girl with the scythe saved them, and Mika agrees to save only those four.

Yu volunteers to drive to meet with them, but Mika decides to drive instead. Mika informs Yu about the Seraph of the End Project, the Hyakuya Orphanage, and how the Demon Army is now redoing the same experiment which caused the end of the world eight years ago. Mika invites Yu to run away with him, and Yu agrees to talk it over with the others since Mika is so set on them. He tells Mika that Mika can trust the others as much as he trusts Yu. Mika says he does not see that happening.

Mika and Yu continue to drive to Nagoya Airport, and Mika once again tries to talk Yu out of it. Mika states that the human named Shinoa is no friend of his. Yu retorts that they have already settled the matter, but Mika says he does not realize how terrible humans can be. Yu reminds Mika that Yu is a human.

Mika says he went overseas a few times to destroy human cults who were experimenting on the Seraph of the End. A flashback shows an emaciated Seraph child with wings for arms confined in fluid with an oxygen mask. It begs Mika to kill it, to "kill this ugly thing I've become."

In the present, Mika states that the Demon Army is the worst of them by far. Yu asks Mika what they should do as an alternative, and Mika they should get away from the Demon Army. Humans across the globe are after the Seraph of the End experiment, and experimental subjects like them would only cause trouble for Shinoa.

Yu agrees and wants to at least check on Shinoa and the others from afar. After that, he and Mika will take off. If Yu's friends are safe, then they can plan how to rescue Guren. Mika immediately turns the suggestion down but soon gives in when Yu begs. He says he may be able to do something if Guren is still alive. Overjoyed, Yu repeatedly asks Mika how until he annoys Mika enough for Mika to tell him to shut up. Mika says Yu has not changed since they were children. Mika says the vampire queen kept him as a pet of sorts, and they can ask her for help. When Yu asks if she can be trusted, Mika says she does not know but will at least listen to them. Yu asks Mika who she is to him, and Mika says she is the one who saved his life. On that note, Yu immediately says they can trust her. Mika asks if Yu has any brain cells in his head at all, and Yu says it was only thanks to her that they could see each other again.

Yu reappears at the end of Chapter 39, just in time to save Shinoa from Kureto's attack. He and Mika step into the fray, surprising Shinoa Squad and Narumi. Mika points out that humans are killing humans and tells Yu they should not have come here, but Yu disagrees. Yu asks Shinoa for orders. She issues a retreat. The survivors all request to be backup for the rear guard, but Mika says he can block chains at that speed on his own. Yu chides Mika on teamwork. When Mika asks Yu if he expects him to trust humanity after seeing them sacrifice their own soldiers like that, Yu says that he is only telling Mika to trust him.

Chains erupt out of one of the trucks. Mika, Yu, and Kimizuki block them. In the midst of the battle between the humans and vampires, Yu flees with the Shinoa squad, Narumi, and Mika while Shinya and the Ichinose Squad cover them. As he is running too far ahead of everyone, Yu sees Guren greet him before the lieutenant colonel suddenly swing his sword at him which is intercepted by Mika.

In spite of Mika and Shinoa's insistence to leave Guren, Yu races towards him while Guren is in the middle of gaining control of the Sixth Trumpet, Mirai Kimizuki. He swings at Guren, but he hesitates and instead demands Guren to explain what's going on. Yu then asks if they were Guren's family which the latter seems to confirm by whispering for Yu to run with tears in his eyes before immediately delivering a deep wound to Yu. Yu is holding onto consciousness as he is carried by Mika and approached by Krul. With Yu secured, she tells Mika to come with her, but Yu insists on saving Guren. When the two disagree with each other, Yu appears face to face with Asuramaru within his mind along with the trumpet from before resting between them. Asuramaru scolds Yu for being so greedy and says he does not have enough power to give them. He calls Yu a traitor and says Yu is betraying him by taking up that trumpet. He says that is the worst decision he could make and says that will erase what is left of Yu's humanity. Yu answers that he does not really care as long as he can protect his family. He blows into the trumpet and is consumed by a massive power that splits the clouds.

Immediately after, Yu violently awakens into his seraph form, the King of Salt, with two wings instead of one now. He flies out of the way of a blast from Abaddon, a demon summoned to possess Mirai, before declaring that the end has come, that tainted humans who dare reach for the forbidden now shall become pillars of salt. Yu then blocks another attack from Abbadon before creating a sword (spear in the anime ) to slice the demons' form.

Asuramaru then appears in front to Yu to remind him that he does not desire human deaths. When Yu asks who the demon is, Asuramaru addresses him as an angel when telling him to be silent. Speaking to Yu within the seraph, Asuramaru says he will help control and contain the seraph if Yu draws his sword to become a full demon. The seraph orders Asuramaru to be silent and says that humanity sees its end today. With goading by Asuramaru, Yu slowly grabs his cursed gear despite the angel's protests, and a pair of horns sprout from his head. He shouts that he is going to save his family and stabs himself through the chest with his own sword. Rendered unconscious, Yu plummets to the ground and is caught by Makoto before being taken away with him, the Shinoa Squad, and Mika.

After a three-month time skip, Mika checks on Yu, who is being held in a building, and asks Yu how he is feeling. Yu's wrists are chained to a wall in a barren room and he has a bowl by his foot. He still has horns and fangs. It seems that Asuramaru has complete control over Yu's body.

Post-Nagoya Arc
Still a demon and chained to the wall, Yu reacts to Mika’s presence and demands to be released. He insists that he’ll kill all of them. He begs Mika to remove his chains, offering he will run away with him and offers his blood. When that fails, he yells at Mika and demands he removes the chains. Mika counts to 120 seconds, and Yu's horns disappear. He mutters about turning into a demon again and greets Mika. Mika states he became a demon for two minutes longer than the day before, which he has been doing since the battle at Nagoya. Mika frets and scolds Yu for becoming something inhuman and doing irrevocable harm to himself.

Shinoa states it has been exactly three hours since Yu transformed and greets them. She mentions it has been three days since Mika drank any blood, but Mika tells her he never asked her to be his keeper. Yu offers his blood, but Shinoa says Yu is too weak and has a bottle containing blood from everyone for Mika to drink instead.

Shinoa examines the chains and says the wards for sealing the demon are beginning to crack, so she and Mitsuba will have to repair them again. Mika accuses her of pretending to be Yu's friend and points out that everything that has happened to Yu has been due to an experiment. Yu says that Shinoa did not get directly involved, but Mika says he cannot trust any of them. Mika asks what Guren did to Yu.

Shinoa tells them they are not themselves when they are hungry and suggests they get breakfast. She holds the bottle of blood out to Mika, but he knocks it out of her hand. Mika appears frustrated, and Yu scolds him. Mika says he is not Shinoa's pet, but Yu says that blood belongs to their friends. A human rushes in asking for help against the Horsemen that are attacking the village, so Yu joins in with this squad to fight the Horsemen to the villagers' gratitude.

Yu then goes to Mika to give him back the bottle of blood, telling him that does not have to drink that blood and can drink his instead. This gets Mika to drink the blood as he fears his worsening thirst would cause him to drink too much of Yu's blood. Yu asks if he is okay with something besides his blood, and Mika says that at least it was not poisoned.

With everyone gathered, Mitsuba summarizes what has been going on: the Japanese Imperial Demon Army will probably hunt them down and kill them, which puts the villagers at risk, they mention they cannot travel overseas because of how acidic and poisonous the blood-red oceans are with monsters even worse than Horsemen swim in their depths. With surrendering out of the question, Yu suggests meeting up with Guren, but Shinoa vetoes that idea and says they cannot trust him.

When asked to share any ideas, Mika suggests that they might be able to trust Krul Tepes, the vampire queen and his sponsor, who also participated in the Seraph of the End experiments. They would need to rescue her which, but it might be their least complicated option. Everyone soon decides to go with Mika's suggestion, so their next objective is to rescue Krul Tepes before Yu becomes a full demon. Yu asks about the best way to rescue to vampire queen as Krul was captured by Ferid. This has Yu recall the events with Ferid that has to lead up of Yu escaping. When assuming that Ferid is probably still alive, Mika points out to him that he saw him back in Shinjuku, but Yu really did not notice Ferid at all as he was so overwhelmed to find out that Mika was still alive and too busy looking at him to notice Ferid.

Yu then notices a strange sound at the same time as Mika, which has the latter tell him that a human-like Yu should not be able to hear that. Mika asks if the demon's possession is advancing even while Yu is awake. Yu answers that it probably is and says his senses are sharper and that he feels a little stronger. Mika is concerned that Yu is really turning into a demon, but Yu blows it off and says that he can protect everyone better if he is stronger. Mika asks what the point is if Yu loses his humanity, but Yu says Mika can hear the sound, too. Since Mika is not human, Yu says this makes them the same.

Informed by Yoichi that its Ferid and Crowley, the squad decides to flee to spare the village. As they are running, Yu asks Mika about Ferid's strength, and Mika says he is probably the second most powerful vampire in Japan. Mitsuba asks if he is even more powerful than the red-haired one, who is a thirteenth progenitor. Makoto mentions that stronger vampires have higher progenitor rankings. Yu states that Ferid is a seventh progenitor, alarming the humans. Yu realizes that Ferid let Yu shoot him and escape to Guren on purpose. Yu considers that Ferid and Guren might have been in cahoots, but Yu pushes that thought away and says that Guren was crying. He recalls Kureto's comment about the Hyakuya Sect orphanages and wonders who is behind it. Since it looks like Kureto was still seeking information about it, Yu believes this was not his plan. He believes Guren could not be behind it either. He thinks about asking Ferid for more information.

Mika realizes Yu is thinking of something dangerous and advises him against it. He mentions going to Ferid's mansion when they were younger and says he still regrets it every day. Yu insists it was not Mika's fault. Kimizuki pats Yu on the back and tells them to quit talking and focus on running. As Kimizuki, Mitsuba, Shinoa, and Yoichi fight Crowley, Yu and Mika agree that they cannot win. Mika advises escaping before they get dragged into whatever Ferid is scheming because there is nothing they can do. Yu wants to stay. He says that every time he runs, his friends and family die. He wants to fight fate. Mika blames himself for doing that once and getting everyone killed, but Yu insists he gave them a future. Yu says they can all make it out alive.

Yu tells Crowley he is surrendering, but Crowley says he is actually not after anything in particular himself.

Ferid appears behind Yu and Mika and nearly drives over them. He jeers that he heard they were being attacked by a dangerous vampire, so he came to their rescue. He says he will save them if they take a ride with him, but Crowley says they already finished that part and surrendered.

Ferid acts shocked and asks when Yu and Mika became so reasonable. Yu explains why they will cooperate, and Ferid asks if that means he will forget everything Ferid has done to them. When Yu agrees… Ferid pulls Akane’s head from his trunk and asks if Yu can say that to her face. Yu turns into a demon, screaming that he will kill Ferid and attacks him. Yu never come close to hitting Ferid, but he manages to slice his fancy foreign car in half. Mika grabs Yu and tells him to calm down. Yu tells Mika to let go before he kills him. He struggles against his demon, telling it to stop while he keeps muttering about killing. Yu struggles against his demon, and Mika orders him to suppress it. Yu tells him to shut up and says he just needs more power. He contacts Asuramaru.

Asuramaru calls Yu a greedy namanari. When Yu asks what that is, Asuramaru explains it and says that this is the third time already. Yu mentions that his memories have been really spotty lately, and Asuramaru says that his human self does not want to deal with the memories of his demon self and hides them away. Asuramaru says that he could take three pills and not die because he is no longer human. Asuramaru asks Yu to let him take over for just an instant. He says he will not kill anybody, but Yu will want to kill all of his friends. Asuramaru says he only needs three seconds.

Yu tells Asuramaru to stop lying to him because he has his own will and knowledge. Yu says he will not become a demon, and Asuramaru asks if that is his human or demon side talking since they are now inseparable. Yu says he does not really care as long as he can protect his friends, but Asuramaru says demons have no friends or family and simply kill everything.

Yu says he supposes he cannot become a demon. When Asuramaru says taking those three pills will make his demon side grow exponentially, Yu shrugs it off, saying it is fine as long as he protects his friends. Asuramaru asks if Yu can hear how much he is contradicting himself.

Asuramaru cuts the conversation short, saying that, this once, Yu will not need the pills because he is about to be rescued by a vampire. Ferid struts toward Yu and Mika, and Mika gets between them, telling him to stay away. Ferid pulls out a filled syringe and asks if Mika will give Yu that dangerous, unstable drug instead. Mika attacks him, and Crowley intervenes, keeping Mika away from Yu.

Ferid says that Yu has grown cute and calls him an “extra-special guinea pig.” He says this curse-suppressant drug is the same drug Guren Ichinose is using. He says he met Guren before the catastrophe when he was just a high school student and received the drug directly from him. Yu demands answers. Ferid says he is cute and bites him on the neck, drinking his blood. He then stabs Yu in the back with the needle, suppressing the demon and putting Yu to sleep. Alarmed, Mika finally leaves Crowley to returns to Yu’s side. He tells Ferid he will never forgive him. Ferid mentions that he just saved Yu’s life as Yu’s blood trickles from his mouth. Mika says they are not going to be part of his plot, and Ferid asks if this is his plot.

Yu eventually wakes up and everyone is relieved to see Yu awake and okay. Mika tells him they are keeping Akane out of his sight. Shinoa says Ferid claims the Seraph of the End experiment was meant to revive the dead. Mika says to not trust him. Yu mentions that the drug appears to be working. Ferid says he has the bodies of the other orphans at his mansion, but he refuses to tell them where they are headed now. Yu says he will not believe a word Ferid says, but he will listen to what he says about Guren.

Ferid mocks Yu about always asking about Guren. The group takes a bathroom break. In the boys' bathroom, Yu rants about Guren taunting them with information but never giving them answers. They tell Yu to quit shouting. Yoichi mentions that Yu has started acting like his old self since he received that medicine. Yoichi says Yu had been acting colder since his demon took over.

They discuss their situation and the Seraph of the End. They decide they must betray Ferid before he betrays them. Mika tells them they are not capable of killing him. Yu mentions that Asuramaru may be able to kill Ferid if Yu lets him take control for three seconds, but Shiho says demons are even worse than vampires. Shinoa mentions they cannot trust a single adult still alive. They crouch together and whisper to come up with a signal of when to attack Ferid en masse.

Osaka Arc
The squad eventually gets back on the bus and are driven to Osaka Bay. When they get close to the destination, Crowley randomly makes an abrupt stop causing Ferid to fly through the windshield and Yu to hit his head. Everyone gets off and be greeted by an army of foreign vampires. Yu accuses Ferid of leading them into a trap, but is promptly warned by the silver-haired vampire to keep quiet or they all could end up getting killed.

After witnessing Ferid nearly turning into a demon when getting his heart ripped out by Lest Karr and then drinking directly from Kimizuki, Yu and the others return to the bus while Mika remains outside to gather information. At some point, Yu asks if they can leave since Ferid abandoned them, but is reminded by Makoto that they are surrounded by vampires.

Yu then offers to go outside to find meat for Kimizuki, which the latter responds by throwing a can at his head, saying he's fine. This is followed by everyone else telling Yu to stop fussing. Yu then turns his attention on Mika, worried about the blonde's safety and noting how he and all the vampires have red eyes. He continues to watch as Mika converses with Lucas and Rene about the vampires retaking Sanguinem.

Yu then notices Yoichi shocked fixation on Lucas and checks on him. Yoichi soon snaps out of it, saying he's fine and is going to take a nap which Yu agrees with. Shinoa then joins him, and Yu apologizes for getting her and everyone else tangled in this mess. Mika then draws Yu and Shinoa's attention to Ferid and Krul being dragged in by Urd and Lest. Yu and Shinoa are unsure of what to make of this. Ferid then sees them and waves at Yu, freaking him out and having Makoto warn him not to wave back.

Yu then watches as Urd sentences Ferid and Krul to be tortured through sunlight exposure for ten days and having them bound to crosses. When he and Krul make eye contact, curse marks appear on his face and Yu finds himself with Asuramaru. Yu asks the demon if he is feeling his emotions, which Asuramaru responds that demons are not supposed to have emotions and doesn't know what he's feeling.

Crowley then comes in and tells Yu that he isn't going to save them right now and neither can he. Yu asks him what he is going to which Crowley responds by asking if Yu wants to save them. Yu stammers before asking Crowley if it hurts which the latter confirms. Mika then approaches the bus and asks what Yu is going to do, and after looking at Krul burning, Yu decides to save them. He asks Crowley if there is a way; the redhead answers that it would be through first taming the Seraph of the End, and they would have to go to Ferid's mansion. Crowley takes Shinoa squad to Ferid’s fifth personal estate in Osaka. Mika asks if Yu is okay, and Yu admits to feeling queasy. Yu says this place looks similar to the one in Sanguinem. Recalling how Mika gave Ferid his blood when they were growing up in Sanguinem, Yu says he should have been the one to give Ferid blood instead of Mika. Mika asks if he would rather Mika be the half-demon instead. Yu says no, and Mika says the two of them are even by now.

Mika asks Yu if he is sure he wants to save Ferid and asks if he can forgive him. Yu says Ferid could bring Akane back to life, but Mika reminds him that Ferid cannot be trusted. He says that if Guren really brought his squad back to life, then the experiment results in the destruction of the world. Mika asks what the price would be if they brought Akane back this time. He advises Yu to not be greedy and want more than what he already has, or else Yu may become a demon like Guren.

Tenth Progenitor Fuola Honte then appears from the mansion and attacks them. Fuola cuts off Mika’s arm off. Alarmed, Yu rushes forward while activating Asuramaru’s power to the breaking point, and ignores Mika’s warning to stay back. Yu blocks the attack and struggles to push it back until Shinoa uses Shikami Doji’s manifestation to grab them and pull them away from Fuola. Crowley then steps out of the mansion and saves the squad by killing Fuola. The group comments on Crowley’s strength. Crowley then spars against the squad and reveals his strength is at the level of a seventh progenitor.

When Mika gets Crowley to reveal that was all due to Ferid’s scheming, Mika repeats that Ferid cannot be trusted. Crowley says he agrees that dealing with Ferid is a pain in the ass, and he suggests they forget about rescuing them. Yu says they already decided to rescue him and says he has things he needs Ferid to tell him. He says he also owes the queen for saving his family. Since they have decided, Crowley tells them they must get stronger quickly since they had difficulty fighting a tenth and must face a fifth progenitor, Ky Luc, in order to rescue Ferid and Krul.

Yu gets mad at Crowley for not telling him he used to be human but Crowley doesn't see the point in telling him. Yu follows Crowley into Ferid's mansion as the rest of Shinoa Squad wonder why he is being so friendly with a vampire, and Mika says its because he is dumb. Yu continues to lecture Crowley but Crowley focuses on a riddle from Ferid. Yu swings at Crowley from behind but Crowley easily blocks the attack and throws his sword into the ceiling. Crowley tells Yu that he is fast but his technique is not. Crowley once again blocks Yu's attack and Yu asks if he trained in swordsmanship. Crowley claims he did when he was human and reveals he used to be a crusader that fought for god, but Yu does not know history so he does not understand.

Yu claims there's something wrong with former humans killing humans but Crowley does not see his point because nothing kills more humans than humans. He tells Yu that he has killed more humans as a crusader than as a vampire. He asks Yu to solve Ferid's riddle and Yu quickly gets the answer is a candle. Shinoa Squad enters the mansion looking for food and Crowley directs them into the kitchen. He realizes it is almost time for Mika to drink but, Mika shakes his head. Crowley tells them they will go into the basement after they eat. Yu asks what down there, but Crowley says he will tell them after they eat. After everyone gets done eating, Crowley reveals to everyone that what is down in the basement are the bodies of their loved ones, and he fears of Yu going berserk and accidentally destroying the bodies. Yu argues with him and Makoto that about wanting to see his family again, and eventually asks Yoichi to give him Akane's head. Seeing her, Yu apologizes to the her for running away by himself and promises to bring her back to life. When warned by Mika of the dangers that promise would do to the world, Yu declares that he doesn't care about the world and will sell it to turn Mika back into a human and save everyone.

Taken down into the basement, Yu cries upon seeing the body of Taichi where is comforted by Mika. He then hears a roar outside, and then minutes later when hearing someone come down the stairs gets ready to attack. Upon seeing that its Guren, Yu frantically asks if its really him in control which earns him a pound on the head by an annoyed Guren and a confirmation for Yu that it really is Guren. He then listens to Guren's reveal on how the Hīragi Family are pawns to another being such as having the Hīragi struggle against that being. Something then catches Yu and Shinoa's attention before the former notices the latter's discomfort. Later on, Yu and his squad mates stop Mika from attacking Guren, and listen to Guren's plan on resurrecting the people that died in the apocalypse.

Learning that Guren's plan involves him, Yu agrees to go with in spite of Mika's protest. At night, after Yu helps Guren carry the latter's teammates into one the mansion's bedroom, he asks and sympathizes with Guren's plight in having to keep secrets from his teammates. Yu then learns that his role in Guren's plan requires him learning to control the seraph by repeatedly take a drug that will make the seraph go berserk until he learns to control it. Just as Yu requests Guren to not tell Mika, the blond vampire reveals that he overheard everything. Yu is next seen in his seraph form bursting through the roof which wakes up Guren's Squad before returning to normal and not remembering what happened earlier. His training lasts three days, and during that time, he listens to Guren's plan on rescuing Krul and Ferid where his role is to kill Ky Luc. Three days later, Yu leaps at Ky Luc the same time as Yoichi firing Gekkoin. After a couple of more attacks from the other squad members, Yu attacks Ky again but now as a seraph to give Guren the opportunity to attack the vampire. Yu then takes a stab to the chest from Ky meant for Guren, but the wound regenerates quickly, and with his time limit in controlling the seraph running out, he contemplates whether or not he should risk using the second dose of medicine. However, with Ferid rescued, Ky chooses to flee and takes Krul with him, ending the fight. Yu collapses with Mika and his squad coming to him.

In his mind, Yu's body under the drug puts him in much strain, and thus does not notice Asuramaru until the it wears off. Yu mentions Asuramaru is upset about the drug, which slows down his demonic transformation, and inquiries what the demon would do if he possessed him. Asuramaru tells Yu he is looking for someone, and he offers to help. Asuramaru then explains to Yu about a buried childhood memory he found, which depicted his talk with Mahiru Hīragi when he was with the Hyakuya Sect.

Yu awakes to Mika calling him, and finds that he is chained inside a liquid-filled container with tubes attached to his body, and his right side has one wing.

After Mika releases Yu from the container, he learns that everyone is asleep, and the two argue over if Guren is good or not. Yu peaks into a room to see others trapped in containers like him, but insists that Guren has good reasons for it. They bicker again, and ends with Yu saying that his demon controls him like Guren's demon, too.

Yu then declares he will do anything to get his family back, that the end justifies the means, and regrets never telling Akane that they were family. Yu and Mika then shake hands.

Yu and Mika are then approached by Guren. Guren takes them to a barrier, and asks if they remember anything the Hyakuya Sect did to them. Yu answers that while his memories were erased, he vaguely remembers being in a cell and meeting a girl, however does not recall who she was.

Despite Mika warning Yu not to follow Guren, Yu says they should, and insists he and Mika go together. They enter the barrier. In shock at seeing the 6th Trumpet, Yu asks what this he is, but then asks about himself instead. Yu quickly summons his trumpet and steps into the barrier.

When the 6th Trumpet realizes that Yu is the King of Salt, he asks why Yu did not destroy the world. Yu requests for the 6th Trumpet to put down his trumpet, and but is told that humanity must be eliminated. The angel calls Yu a traitor and sends Horsemen at him. Yu deflects them with his trumpet, and slashes the 6th Trumpet's chains. Yu repeats that he will save him. However, the 6th Trumpet states that he'll be the one saving Yu, to remind him of his "true mission".

The 6th Trumpet blows his trumpet, and more Horsemen rise up from the ground. Yu exchanges his trumpet for his sword and cuts them apart. The 6th Trumpet says that Yu's weapon can't damage his trumpet, but the trumpet gets nicked, which causes an explosion. With the 6th Trumpet now in the air, Yu manifests his wings and they take it to the sky.

As Horsemen emerge on the mountains, Yu shouts at the 6th Trumpet to stop blowing his trumpet. He says humanity has suffered enough, and asks if being punished even more is necessary. The 6th replies that they have committed a sin that cannot be forgiven, but Yu counters that he and others alive have done nothing to deserve this.

The 6th Trumpet claims that Yu's existence is forbidden and must be destroyed, and attacks him. Yu demands more power from Asuramaru, who asks why he wants to save a stranger such as a the 6th Trumpet. Yu responds that he is an angel like him, and then realizes that the 6th has a demon. Once Asuramaru notices it himself, Yu convinces him to keep hanging on longer.

Yu sees his squad in the forest and calls to Kimizuki, ordering him to give the drug he has been using to the 6th Trumpet. When Kimizuki is concerned about Yu's power output, Yu says he is going to save everyone and live. As the battle continues, both of Yu's sclera turn black, hands grow claws, and now has four wings instead of two. The 6th repeatedly demands Yu to die, and Yu eventually tackles the angel, pining him down. Mika deflects the trumpet from attacking Yu, and Kimizuki injects the 6th Trumpet with the drug. Kimizuki and Yu catch 6th after he falls. Though unsure if the seraph is alive, Yu celabrates their victory, and the squad meets up after.

Shibuya Arc
Yu calls to Shinoa who is currently undergoing the transformation into a vampire. He is pushed away by Kureto and told to get lost and watches as Shinoa is removed to an examination room. Yu asks if Kureto can save her blaming himself as Shinoa let that monster possess her to save him. He confirms with Kureto that he met that thing, that it knew him and Asuramaru from some time ago. Focusing only on helping Shinoa, Yu speaks candidly despite Mika prodding him to not hand out information that he is sharing for free. Though Yu does not remember anything, in order to save Shinoa he offers himself for examination to uncover potentially helpful memories. His offer is accepted, at once being taken away by Kureto's guards where Yu is verbally robbed of his freedom and declared an experimental subject. Yu accepts anything they want to do to him, so long as Kureto swears he will save Shinoa before being led away.

Yu from history is remembered by Urd Geales beside the first when he was alongside Rigr Stafford.

Back in the present, Yu struggles against the two guards taking him away. He demands they forget about him, and to promise to find a way to keep Shinoa from turning into a vampire. His sword has been taken as Yu tells them the monster knew them both from ages ago. and continues to protest as he is trailed by Mika.

He awaits on a stretcher with Yoichi, Mitsuba, Narumi with Kimizuki nearby as they hear what sounds like a battle. Yu asks what nearby scientists are waiting for, shouting that he is supposed to have info on that monster buried in his memories. He tells them to hurry up, as if that thing takes over Shinoa it will be too late. Aware of the electrical needle being moved towards his neck, Yu reassures Mitsuba who has remained behind with him that he will be fine and that she should go be there for Shinoa. Yu firmly tells the scientists to go ahead, he needs to remember what he knows of that monster so he can go save Shinoa before having the needle stabbed into the back of his neck and his eyes change dramatically. Unconscious, he is unable to help Mitsuba who has been attacked by the very scientist helping unlock Yu's memories. Revealed to in fact be a member of the Hyakuya Sect, Yu is taken to a new area via a tear in reality. In his mind with Asuramaru, Yu lays on the ground with two spears in his back as he faintly tries to remember.

Unconscious, Yu is brought by the agent before Saito who orders him to be taken to their lab in Ikebukuro. With the Hyakuya Sect's attack on Shibuya in full swing, in the north ward of the city Yu is chained and being transported on a stretcher. He wakes up to witness the fight between Saito and Shikama Doji who is inside Shinoa's body. Noting the explosions he asks why is he tied up, he cannot get them off. Addressing those pushing him along he asks where are they taking him as he continues to be wheeled though the streets of Shibuya with his sword transported on another stretcher nearby.

Natural Abilities
Yūichirō is an excellent swordsman, being trained by Guren himself. He is capable of easily taking down Horsemen with both an enchanted gear and Cursed Gear blades, and has proven to effectively fight and slay common vampires. Yet another testament of his skills is that with just a regular blade, he was able to go up against Shinoa using Shikama Doji, which earned him her praise. Along with that, he can even take on Guren himself in a sword-fight, although not enough to actually match him equally as Guren was holding back due to it only being training, as he was easily defeated by Kureto, a swordsman who was, although only by a slight margin, inferior to Guren in terms of skill. Nevertheless, he earned praise from Aoi Sangū for his sword skills, pressuring her when she blocked his attempt on Kureto's life.

He is also a "Seraph of the End" hybrid with 1/10th of him being not human due to him and his old family being experimented on by the Hyakuya Sect. After he overdoses on the curse supplement to save Guren from Crowley, his non-human part increases.

Enchanted Gear
Mass-produced cursed gear, these demon weapons are much weaker, usually of the yaksha or myo-o series, as they increase a regular human's strength by three to four times. Yu wielded one in the form of a katana, and was able to use this gear to easily slay a horsemen and hold his own against the escaped vampire, Noin Teta.

Cursed Gear
These weapons are capable of increasing a person's strength by seven times.
 * Asuramaru (阿修羅丸): Asuramaru is a possession-type demon weapon of the Black Demon Series, where he takes the form of black katana with a green edge. Whilst in use, the blade develops a thick green aura. Like Mahiru Hīragi, he can call upon Asuramaru to fully use its power to attack opponents.
 * Asura-Kannon: A special technique using Asuramaru that materializes dozens of floating swords.

Experimentation

 * Drugging Up: Like other soldiers in the JIDA, Yu takes a supplement to increase his synchronicity with his demon to 150% for 15 minutes. After that time is up, this synchronicity drops to zero. There are numerous unpleasant side-effects, and officers only resort to this as necessary.

By using the golden trumpet within his consciousness, Yu undergoes a drastic transformation. As a completely awakened Seraph, he is the Second Trumpet referred to as the "King of Salt" (塩の王). His main power consists of turning every living being into pillars of salt. Additionally, he can also create a spear made of salt that can block Abaddon's destruction ray. He later has full control of his Seraph state.
 * Seraph of the End: By swallowing a special tablet produced by Guren, Yu can lose his mind and undergo a painful transformation. Although extremely powerful, he goes berserk and attempts to kill any human nearby. Guren causes this transformation to end by making Shinoa hug Yu. The transformation ceases, and puts Yu into a coma for a week. It takes five days for the drug to get out of Yu's system, and even after that, he feels tired. Yu has no recollection of the events that occur while he is transformed.


 * Anime: He attacks both vampires and humans without discrimination while he only wants to kill humans in the anime and orders vampires like Mika to get out of his way. Additionally, his power is demonstrated more in the anime when he swings his sword and creates a plume of black energy the size of a tall building with a ring of light around its base.

Book 5

 * "Who are you? Are you here to kill me, too?"— To Mahiru upon meeting her the first time, Prologue


 * "But I don’t! My mom and my dad said so! They said that I was a demon and needed to die! That as long as I live, bad things will keep happening… so instead I need to die! My dad was always so nice to me, but then he pulled that knife out… And then my mom said I shouldn’t be alive anymore. She said I’d be happier dead. Because I’m a demon, a monster, and I’ll ruin the world… It’s… It’s my fault that they’re dead… Mommy! Daddy!! Ahhh!"— To Mahiru, Prologue


 * "B-But… How is someone like me living worth anything?"— To Mahiru, Prologue

Trivia

 * Yūichirō 「優一郎」 translates as "kind first son."
 * His parents spelled it with the kanji for "gentle" in the hopes that he would grow up to always be kind and gentle to whomever he met. Mahiru believes this idea is ludicrous for anyone less than a god.
 * Due to Yu's name, it is considered a pun when other characters say Yu is kind (優しい). Kindness is also considered one of Yu's actual primary character traits.
 * Hyakuya 「百夜」 means "hundred nights."
 * Amane 「天音」 means "heavenly sound."
 * He was one of the first characters designed, along with Mikaela and Guren.
 * Yūichirō is the only member of Shinoa's Squad who does not have a known biological sister.
 * In the Michaela light novels, Mika asks Yu what his surname was, but Yu can no longer remember that his name was Yūichirō Amane and solely goes by Yūichirō Hyakuya.
 * When Yu first forms a contract with Asuramaru, it is revealed that 1/10th of him is not human. He becomes even less human in chapter 34 after overdosing on curse stimulant pills. At the end of chapter 40, he chooses to erase his humanity completely.
 * Since he lived in a vampire city for 4 years, Yu is nearly illiterate and only writes phonetically without using any Kanji. Vampires have no need to educate livestock on how to read or write.
 * Mika is the first vampire shown to bite Yu. Yu offers his blood three times before he finally convinces Mika to bite him in chapter 36.
 * At the age of twelve, he was 145 cm tall and weighed 38.2 kg.
 * According to the Q&A with Kagami, Yu's seraph form has black wings because his demon tries to stop the transformation.
 * In the popularity poll, Yu earned 3rd place at 3,536 points. In the 2019 popularity poll, Yu ranked 1st with 8,886 votes.
 * According to the Manga 8.5 Fanbook:
 * Interests: Worrying about Mika / Driving cars.
 * Favorite Food: Curry, Shortcake (because the children at the orphanage said they wanted to try birthday cakes).
 * What he looks for in the opposite sex: “Shut up.”
 * According to the TV Anime 108 Fanbook:
 * It's been stated that Yu 's favorite color is blue because it reminds him of the blue sky he saw once he escaped from Sanguinem.
 * Yu's favorite pajamas are yellow.
 * One of Yu's dreams is to drive a fast car.
 * Yu's goal after saving Mika is to eat curry.
 * Yu does about ten push-ups and additional training daily.
 * In his previous life with Ashera it is shown that he already has Seraph powers as the latter grew angel wings behind his back.
 * In one of the OVA's, Krul whispers in Mikaela's ear that Yu is a **********, and by the creators of the show later translated this to "Yu is a homosexual", although no other evidence has been provided to prove this point besides in the OVA.