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 the 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, he becomes a hot-blooded youth with a kind heart. which shows when in his fearlessness and somewhat reckless actions show when he attacked a Horseman while ignoring orders, and is noted 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," and he will overcome any type of challenge in order to accomplish it. He swore to exterminate all vampires for killing his family, especially Mika.

Despite this, he has a soft spot and worries about his friends first and his goals second. Ferid Bathory considers this attitude to be "cute". Because of this, he 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.

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.

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.

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.

Natural Abilities
Yūichirō seems to be an excellent swordsman, as he was trained by Guren himself. He is capable of taking down Horsemen with both an enchanted gear and Cursed Gear blades, and has proven to effectively fight and slay common vampires.

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.

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.
 * 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.

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