Yūichirō Hyakuya

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 manga. 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.

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 a 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 was 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 became 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 teenage years, Yu started off as moody and antisocial due to the tragedies during his childhood. 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 becomes 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 orphans, 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 expresses 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, but he does tell a vampire to not interfere. 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."

During the Dark Ages of Greece, he possessed Seraph wings for flight, and also displays the same murderous behavior as the current Yu when being the Seraph of the End.

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 persuade Mika with his blood and promises to run away with him if only Mika will set him free.

Thanks to Shinoa and Mitsuba's wrist 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.

Story
For the total coverage story detailing Yu's history as well see:

Yūichirō Hyakuya was brought to the Hyakuya Orphanage after his parents attempted to murder him and there meets Mikaela Hyakuya as well as other orphans that lived there. An apocalyptic event occurred where the adult population perished and vampires emerged to gather the surviving children. Yu was taken to an underground vampire city where he lived for the next four years. Discontent with living there Yu would realize that Mika was giving his blood to vampire noble Ferid Bathory. Angered further he would tell Akane Hyakuya that he had no family. His desire to leave the city would result in Mika bringing back a map with an exit to the city. The plan for Yu and the orphans he lived with to escape would be successful until the end where at the exit Ferid revealed it as a cruel ruse and set about murdering the orphans. With Mika sacrificing himself Yu reluctantly left him behind to escape having recognized they were his family. Outside he would be found by Guren Ichinose and swear vengeance against vampires.

Four years later Yu patrols outside as a scout but with an unwillingness to work with others he is suspended until he can make a friend in the education system. He is monitored by Shinoa Hīragi where at her urging he helps Yoichi Saotome against bullies and engages an escaped vampire. After coming into contact with a cursed gear weapon and overcoming a demon that had taken the form of Mika and their orphanage family, Yu was told he would be able to join the vampire extermination unit. Coming into conflict with Shihō Kimizuki he would continue training until selected to choose a black demon ranked cursed gear. The sword he touched would bring him into contact with Asuramaru whose strength Yu needs to enact revenge and protect others. Haunted by dreams of Mika asking why he left them behind Yu would head out of the city to track vampires and have Mitsuba Sangū become the fifth member of the squad. After rescuing a child from a Four Horsemen of John and resist the following vampire trap Yu would locate their stronghold and free the humans kept there.

Proceeding to Shinjuku Yu finds it under attack and outside the walls confronts a vampire noble, Crowley Eusford who is joined by Chess Belle and Horn Skuld. Within the city Yu would stab a vampire who had Guren cornered to then realize that it was Mika who had survived. Yu would transform into a monstrous one winged being and then pass out. With the battle won in humanity's favor Yu was relieved his squad and now Mika were alive. Determined to rescue Mika from the vampires Yu would be summoned by Kureto Hīragi of the Japanese Imperial Demon Army. With rapid advancements in battling capabilities Yu would hear from his squad that he had likely been experimented on and that it was possible Guren was using them. He decided to stick with Guren as a part of their family.

Before a campaign to eliminate vampire nobles in Nagoya Yu would find his own prowess and team work lacking. Along with Makoto Narumi's squad and Shinya Hīragi they would collectively defeat fifteenth progenitor Lucal Wesker. Other missions across the city were not so successful and Yu would take part in rescuing hostages captured by Crowley and the vampires under his command. After a rescue attempt involving Guren, Yu would become a partial demon before being having to be rendered unconscious by his team with vampire reinforcements arriving. Carried to the airport Yu would be retrieved by Mika. Upon awakening he was further warned that the humans were using him yet Yu would not entertain the matter until Mika drank his blood to survive his injuries. With Mika he arrived at the airport to find the survivors of the mission being executed by Kureto and defend his squad from the army and an incoming fleet of vampire forces. The experiment culminated into a seraph gaining consciousness in the world which summoned the demon Abaddon. In an attempt to save everyone Yu resorted to the inhuman power within himself and as the King of Salt was able to vanquish this threat.

Three months later after escaping the army and vampires with Mika and Narumi as well then living near the ocean Yu would be afflicted by prolonged durations of becoming a demon. With finding Guren and Kimizuki's sister Mirai Kimizuki a goal Yu agreed with Mika's plan to rescue the vampire queen Krul Tepes who was betrayed by her own kind to assist with this. Yu and the squad in turn would be located by Ferid and Crowley where unable to defeat them had little choice but to adhere to their plans. Seeing Ferid reveal Akane's head would result in Yu succumbing to his demon of which the problem was dealt with using a syringe Ferid had. Travelling to Osaka Bay Yu comes across a huge number of vampire nobles who have arrived in Japan from foreign countries. With Ferid and Krul sentenced Yu heads to Ferid's mansion with Crowley since using the Seraph of the End power is all that can be resorted to in order to save who they need. After finding his deceased orphanage family members kept in containers there Yu would also be joined by Guren.

With one noble, Ky Luc, guarding the bound Ferid and Krul, Yu would join in the attack to free them where he could deploy his abilities as a seraph which resulted in Ky Luc retreating with Krul. A childhood memory surfaces involving Mahiru Hīragi and Yu awakens at Guren's residence. There another seraph is kept who views the King of Salt as a traitor for not destroying the world. Coming under attack Yu manages to subdue the seraph. Joining Guren with the squad at Shibuya Yu offers his memories if they can help Shinoa against her demon Shikama Doji who is decidedly a threat to them. After he is led away Yu is kidnapped by a member of the Hyakuya Sect that has launched a stealth attack against the city. Finding himself being strapped and wheeled away on a stretcher Yu is saved by Mika before seeing a horned Guren before him. They come under attack by Guren and his demon. Although he is half possessed and manifests some formidable powers Yu is unable to stop himself being neutralized as a threat neither can he stop Mika from being hurt. Crying as Mika rises into the air Yu witnesses a explosion envelop Mika. He is unwilling to leave until persuaded to by Krul who arrives and states that Yu can save Mika later if he leaves now.

Some distance away from Shibuya Yu has escaped with his squad and Krul. He sees that Shikama Doji is in control of Shinoa's body as Guren joins them shouting for Yu to turn Mika into cursed gear.

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, later he can hold his own in a sword-fight with Guren, although not enough to actually match him equally as Guren was holding back due to it only being a training exercise. Yu 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.

Upon synchronizing with his Demon his own strength has skyrocketed, although he has yet to control it with his Demon as his own mind went fuzzy and is unstable, but he has demonstrated new techniques.

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.
 * Asura-Kannon: Thousand Blades: An advanced type of Asura-Kannon, where a warped space is formed and expand around Asuramaru, which thousands of swords materialize and surface from the warped space with a homing effect at the target.
 * Asura-Kannon: Ten-Thousand Blades: Knot of Fate: When used the original warped space range widens, able to cover an entire building, and millions of thousands swords surface from the warped space which materializes with a homing effect at the target. It has enough destructive force to shatter the surrounding area in the warped space.

Experimentation

 * Cursed Gear Stimulants: 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 including ones internal organs exploding, and officers only resort to this as necessary.
 * 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. Later he would be able to control his own Seraph on his own.


 * 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.


 * Immense Physical Strength: As seen during his fight against Ky Luc, while in his Seraph form, Yu possess tremendous physical strength, as seen where he was able to physically damage and even break the limbs of a fifth Progenitor Vampire, greatly surprising Ky and making him actually doubt if he could overpower and defeat him.
 * Prehensile Tongue: While in this form, Yu's tongue becomes black, extendable and incredibly sharp, with him having been shown to use it to injure and cut Ky Luc.
 * Regeneration: While in this form, Yu's regenerative powers are also boosted to the level of Vampire Nobility, as seen where after Ky Luck's pierced his chest, crushed his heart and left a fist sized hole in his chest, Yu was able to not only survive the wound, but completely restore his lost organs in minutes.

Book 5
"Who are you? Are you here to kill me, too?"

- Yu to Mahiru upon meeting her the first time.

"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!"

- Yu to Mahiru.

"B-But… How is someone like me living worth anything?"

- Yu to Mahiru.

Seraph of the End: Vampire Reign
"GAH! I CAN'T TAKE THIS ANYMORE!! It hurts! It makes me dizzy! And I can't stand those blood-suckers looking at me like I'm livestock! What do they think we are? Pigs? Cows? Chickens?! That's why we've gotta start a revolution! You and me, Mika. We'll both get stronger, and then we'll go kill the vampire queen and turn this place into a human kingdom!"

- Twelve-year-old Yu to Mika in the streets of Sanguinem.

"Who needs some stupid 'family'? I got sent here because my father tried to kill me. My mom kept ranting and raving about how I was demon spawn. She eventually went nuts and killed herself. So do you get it now? 'Family' doesn't mean anything to me!"

- Eight-year-old Yu to Mika the day Yū arrives to the orphanage.

"Quit trying to shoulder all our burdens by yourself!"

- Twelve-year-old Yu to Mika in Sanguinem.

"You're... my family. I... finally found a real family! I can't leave you!"

- Twelve-year-old Yu to a fatally injured Mika.

"Every time I close my eyes, I see the same scene. I'm back in the underground world ruled by vampires... watching my family die. I'll make them pay. I swear, someday I'm gonna make them pay. I'm gonna find those bloodsuckers... and kill them all!!"

- Thirteen-year-old Yu's thoughts.

"Gimme all your weapons!!"

- Thirteen-year-old Yu to city guards

"No more... I said I don't have any of those anymore!! You know what happened! My parents abandoned me!! I finally found a second family at my orphanage, but then they all got killed by vampires!! Anybody that I even start to like dies!! How am I supposed to find anything to protect anymore?!""

- Thirteen-year-old Yu to Guren.

"You aren't Mika. Mika would never tell me to get revenge. He was smart, but he was always stupidly nice to all of us. SO WHO ARE YOU?! HOW DARE YOU PRETEND TO BE MY FAMILY!! I'LL KILL YOU!!"

- Describing Mika to a Myo-o demon and angered it would take his form.

"ARE YOU STUPID?! WHO CARES ABOUT POINTS?! THIS IS YOUR FAMILY WE'RE TALKING ABOUT! If they die, then... they're gone for good. You won't ever see them again."

- Yu to Shihō Kimizuki when told that Mirai Kimizuki is in critical condition.

"Once I have the power, I'll get revenge for the death of my family. Those bloodsuckers killed Mika, so I'm gonna kill them all!! That's my one and only reason for living."

- Yu before first challenging Asuramaru.

"DAMN IT!! SHUT UP, SHUT UP, SHUT UP!! Just give me your power already!! I... need it!! I need enough power to protect everyone!!"

- Yu confessing the truth of his feelings while confronting Asuramaru.

"I don't ever wanna say I survived because I left someone else to die ever again!!"

- Yu to Shinoa's squad when he enters an obvious trap to save a human girl.

"What was it you guys said? We humans are 'ugly'? Trash that would sell out anybody if our family's been taken hostage? Ha! Sounds like you're real familiar with that little ploy. You're right. Humans will do anything for their families. We'll happily lie, cheat, make deals with the devil, or even become demons ourselves. If you wanna call that 'ugly,' then fear human ugliness when it kills you, Bloodsuckers!"

- Yu to the enemy vampires in Omotesando Station.

"...'Those humans' are using me? What's that mean, Mika? You... You make it sound... like you aren't human anymore. It's my fault, isn't it? My fault for running away..."

- Yu to Mika when they reunite.

"S-s-ssi-sinners... S-sinners must... d-die. M-must kill... all s-si-sinners."

- Berserk Yu preparing to kill Shinoa.

"Do not interfere, Vampire. All humans must be killed."

- Berserk Yu speaks nonviolently to Mika when he protects Shinoa.

"It wasn't a dream. And that means Mika really is alive. Ha ha... He's alive... Ha ha ha... I'm not dreaming... He really didn't die... Thank God... I'm so glad!"

- Yu to himself, after waking from a coma.

"Just you wait, Mika. I swear... I'll save you."

- A vow to himself.

"...I was looking west. That's where Mika's gotta be, right? In the vampire city. I heard the place they held us was somewhere underneath Kyoto... Someday, I swear... I'll go get him back."

- Yu to Shinoa when asked what he was looking at.

"Whatever your reasons, if you hadn't rescued me that day, I would've died. I do still feel like I owe you for that. So what I wanna know is... Am I actually useful to you? That's all. I don't care what you and that Hiragi guy are fighting about. I don't care what you're after. All I want to know is, do you need me? If you do... Would you want Mika, too? He was in the same orphanage as me. If you do... If you think you could need Mika like you need me... Then, I'll be your guinea pig or anything you want. I'll do everything I can to help you with whatever you need. Just tell me how I can get Mika back!""

- An attempt to involve Guren in Mika's rescue.

"Those words don't hurt me anymore. Besides, I don't care if I am demon spawn. If Mika needs me.. If Guren, Shinoa, Mitsuba, Yoichi, and Kimizuki want me as their friend, then I don't care if I'm a demon."

- To Asuramaru and unconcerned about being a demon.

"I don't care if you're a demon. I need you, Asuramaru. Join me, please. We can be friends. Help me rescue Mika... He's family."

- Requesting Asuramaru's help in a different manner.

"I... Um... This is kinda embarrassing, but... Well... Guren said we're family now, right? So you, Yoichi, Kimizuki, and Mitsuba... We're all a new family. And I've started to feel that's true. You guys are important to me. But... I can't forget Mika. He's also an important family member. See... My parents abandoned me. So maybe I don't really know how families work. But can I ask you guys this? Just because someone in your family betrays you, does that mean you have to betray them back? I don't... think it works that way. So even if Guren betrays us... and Mika, well... even if he is a vampire now... he's still family. We're all still family, and we always will be."

- To Shinoa squad when deciding who to ally with.

"So, if it's for the mission... should we have to ignore our feelings and abandon family? But, Shinoa... If we do that... If we just give up on family in this empty, ruined world... Then what? What else is there... to cling to for survival out here? Guren... He... He's our family!! Crap. I can't do it. Sorry, Guys. Looks like I'm just not cut out for that teamwork stuff. You all go on ahead. I'm gonna stay here. If I can't save my family... I'd rather die anyway."

- Yu to the Shinoa and Guren Squads before overdosing on curse stimulants.

"Why'd you save me? I... I don't have a family anymore... I haven't since I was born, really. My parents called me demon spawn and tried to kill me... I made a new family, and then they all got killed too. After all that... What's the point in living? Is it really worth it... for me to even bother?"

- Twelve-year-old Yu to Guren in a flashback.

"NO!! DON'T YOU DARE GIVE UP!! YOU... YOU WERE THE ONE WHO TOLD ME I HAD TO LIVE DESPITE ALL THE PAIN!! SO BE A DAMN ADULT AND BE A GOOD EXAMPLE FOR ME!!"

- Yu to Guren before becoming possessed.

"Mika, whoa! It's me! Yu! Don't you recognize me?!"

- His reaction to Mika attacking in a state of blood lust

"Who cares about that right now?! You look like you're about to die, Mika! What can I do?! How can I help you?! It's blood, right? Will you heal if you drink some? Then, go on and drink mine! Here! Take it!"

- Offering blood to help Mika.

"If you up and die on me again... I... I'll cry, you moron!! So live, dammit! Even if you have to turn into a vampire! Even if you have to crawl through the mud on your hands and knees--live!!"

- Trying other means to persuade Mika to drink.

"LA LA LA LA LA!! I can't hear you!! Who's gonna pay attention to some dumb idiot who just gives up on living like that! If you want me to listen, drink my blood first. If you want to save me, then let me save you first. You aren't going to die, Mika. I won't let you."

- Yu to Mika.

"Hah! Don't be stupid. Just drinking a little blood isn't enough to make you a monster. No matter what you are, we're still family."

- Dismissing Mika's concerns about feeling a monster, where it would not matter even if it were the case.

"Welcome home, Mika."

- Yu to Mika after Mika bites him.

"Years ago, Guren told me something. Oh! You wouldn't know him. He's the guy who took me in after I escaped on my own. I'd just lost all of my family. I was hurting so bad inside, and I wanted it all to end. I wanted to throw it all away and give up on life. But he told me that, even if my only reason was for revenge, I should live. So then... Maybe someday, somewhere... I'd find somebody who would need me again. So I gave the whole living thing a chance. Even though I figured no one would ever need me, I kept surviving. Struggling, flailing around like a total idiot... But apparently I kept at it long enough that I found you again. Mika... let's live on together, okay?"

- Yu to Mika.

"I died long ago on the day my parents abandoned me. But then you helped me live. And after you, it was Guren. Somehow, thanks to you two, I'm still here. And in that case, if either of you want to use me... fine. Go ahead. I don't mind."

- Telling Mika how he felt after his parents left him.

"I said I wanted to rescue my family. So I'm going to rescue them. And you're obligated to help me."

- With Mika safe Yu intends to rescue his squad with Mika's help

"What? Run away to somewhere both the vampires and the Demon Army won't ever find us? Man, that brings back memories. Back then we were both desperate to run away from our world of vampires and slavery. So we escaped... Hoping and praying to find some paradise where we could live in peace... But all we found was this. We can't run, Mika. There's nowhere to run to. No matter where we go, all we'll find is more humans and vampires."

- Considering escaping with Mika with the realities at hand.

"Yeah, yeah. Say that all you want... I'm still a human myself, y'know."

- Yu to Mika after Mika keeps harping on how terrifying humans are.

"Well, without her saving you, we never would've seen each other again! It's only right to be thankful to her for that."

- A favourable view of Krul Tepes spoken to Mika.

"Shinoa, I have no idea what's going on here, but we're all gonna help each other get out of this alive. Shinoa, what are our orders?""

- Reaching Nagoya airport where soldiers are being attacked and turning to Shinoa as the squad leader, Chapter 40 "Trumpet of the Apocalypse"

"I swear!! I'm gonna get us all outta here!! And I won't let any of you die!!"

- Meaning to help his squad escape the Japanese Imperial Demon Army and vampires.

"This... This can't be happening. Tell me this isn't happening, Guren. You'd never betray your friends and family, right?! There has to be a good reason for this!! Say something! Anything!! Guren!! Weren't... Weren't we... Weren't we your family?!"

- Trying to understand Guren for attacking.

"Mika... Guren... H-He was crying... We have to save him...""

- Telling Mika he feels Guren is still in there

"As long as I can protect my family, I don't really care."

- Yu opts for the trumpet over Asuramaru's power and lose his humanity altogether.

"The end has come. Tainted humans who dare reach for the forbidden... May you all become... PILLARS OF SALT."

- Yu awakened as a seraph.

"The end has come. On this day, the cycle of human greed and desire... shall crumble... as naught but pillars of salt in the wind."

- Yu as a seraph.

"SILENCE!! HUMANITY SEES ITS END THIS DAY!!"

- Yu as a seraph to Asuramaru.

"STOP!! Cease this, humans!! Do not reach further yet into the forbidden!!"

- Yu as a seraph before becoming a demon.

"LET ME GO!! UNCHAIN ME RIGHT NOW!! I'LL KILL YOU!! I'LL KILL ALL OF YOU!!"

- To Mika after becoming a full demon.

"Please... Mika... Take these chains off of me, wouldja? C'mon. We'll run away together. Just the two of us... You and me... We're the only family we've got. Right? ...Oh, I know! You've got to be getting thirsty, right? You can drink my blood. Then we'll run away together. We'll run away from all the humans... and all the vampires, and go live in peace—just the two of us. Isn't that what you want? ...C'mon, Mika. They hurt. Really. Take these chains and wards off. Please, Mika. DIDN'T YOU HEAR ME?! I SAID TAKE THESE DAMN THINGS OFF OF ME!! TAKE THEM OFF!! GET THEM OFF OF ME NOW!! I'LL DEVOUR YOUR ENTIRE SOUL!! Buh? Oh. I guess I turned into a demon again. G'morning, Mika!"

- As a demon he remembers Mika's desires before changing to anger then back to himself.

"Those 'stupid humans' are all your friends now, y'know."

- Informing Mika on Shinoa Squad's status.

"Ferid... He's the one who split the two of us up... and... killed Akane and the rest of our family.""

- With Mika recalling the consequences of Ferid's actions

"Ha ha ha... I was just so overwhelmed that you were still alive and all... I guess I was too busy looking at you to see anything else."

- Saying to Mika about why he never noticed Ferid in Shinjuku.

"I guess that makes us the same!""

- Unbothered about losing his humanity and helping Mika feel better about his state of being.

"Hey, Mika? Do you think Ferid let me escape on purpose?""

- Discussing matters with Mika and considering the reality behind himself shooting Ferid and escaping Sanguinem as a child.

"This was planned. All of it. From the beginning. Then... When I got out of the vampire city... The fact that I came across Guren right away was... No...! Guren cried. I saw him crying...! Is he somehow tangled up in this whole thing, too? But whose plan is it? ...So did this plan start before the catastrophe? In that case, Kureto Hiragi can't be behind it. He sounded like he was still looking for information about it. Guren can't be behind it either. Is it Ferid? It might be worth talking to him at least once..."

- Yu's thoughts and considering a bigger picture.

"No. That wasn't your fault. Since before we were born...we've been caught up in someone else's plot. That's why every time I run, my friends and family die. I'm sick of it. This time, I'm going to try fighting fate."

- Easing Mika's guilt and deciding to change his course.

"No! What you did gave us a future! Because you found us a map! You found us a way to quit being livestock—"

- Supporting Mika's previous plan.

"No, you listen! This time, we do it together! It won't be just you. We'll both leave. We'll both get out of this screwed up world together! Let's do it again. Let's go find our map out of here. Together. And this time, all of us...will make it out of the dark alive."

- Beside Mika and not intending to have him shoulder everything by himself.

"Just now. If we're after the same thing...I don't mind allying myself with you.""

- Unable to win in combat Yu presses for an alliance with Ferid

"Th-this is bad. Really bad, Mika. I... I can't hold it back... I'LL KILL YOU!!"

- To Mika and then Ferid after he loses control over his demon side when Akane's head was shown.

"Who does that bastard think he is?! First he goes and says that it's Guren who destroyed the whole world, but now he won't tell us anything else!! That snarky, smug, grinning bastard!! He needs to stop beating around the bush and tell me everything right now!!"

- Ranting about Ferid.

"Be grateful we have comrades at all."

- Yu to Kimizuki.

"I hope Mika will be okay... Look at them. They all have red eyes. Even Mika."

- From within a bus Yu observes Mika speaking with other vampires

"The rescue is already decided. There are things I need Ferid to tell me, and I owe the queen for saving my family. So we rescue them."

- Saying to Crowley on why he needs to help Ferid and Krul.

"Hrm. Hang on a sec. Just in case... Lemme calm myself first.... Akane, I'm sorry. I'm sorry I ran away all by myself. But I promise you, I'll definitely bring you back to life."

- Taking possession of Akane's head.

"I don't give a crap about the world. I can understand how Guren must've felt.""

- To Mika when Mika warns him that reviving the dead will destroy the world.

"I know. And I want to save you. I promise you, Mika. Even if I have to sell out the whole world to do it, I'll make sure you're turned back into a human. Akane. The other kids. Narumi's family. Kimizuki's sister. I'll bring everyone back."

- Yu to Mika and their squad.

"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."

- Concern for his squad over himself.

"Like I care. I'm going to get our family back, and I'm totally willing to do anything to do it, too. The end justifies the means! That day, I wasn't able to admit to Akane that we were family. But next time.. The next time I see her, I'll say it. If I get another chance, I'll tell her that we're family. And to get that chance, I'll do anything. Even if it means killing people, I'll do it. I'll do whatever it takes to protect my friends and my family. That's what it means to be human. Right, Mika?"

- Remaining determined Yu explains his goals to Mika.

"No. We go together. I'm sure we'll be just fine as long as we're with each other."

- Yu to Mika.

"Y'know, I don't remember much about when I was a kid, either. I wonder what's up with all this amnesia everywhere...?"

- Yu to himself

"I'm Mitsuba's family. The only thing we lay down our lives for is the rest of our family. Your stupid cause can go jump off a cliff for all I care."

- Yu to Aoi Sangu when she tells her sister Mitsuba that she has no value.

"I hear the Hiragis are supposed to be doing all kindsa super incredible, super dangerous, super evil research. Mebbe they've got something we can use that'll be all like, poof! You're human again! Just like that! And poof! I can perfectly control my demon and my angel, too! Like a magic wand! And theeeen... Maybe we'll find something that let's us do the forbidden—bringing the dead back to life. We'll bring Akane, the kids, and everyone else back. We'll do whatever it takes... And make any sacrifice we have to make. Any sacrifice."

- Hearing of and encouraged by what he knows of the Hiragi family said to Mika.

"I don't really care about my memories. I have friends now. And family! If I have them, I don't need anything else!"

- Divulging to Shikama Doji what is important to him.

"Forget about me! Just promise me you'll find some way to keep Shinoa from turning into a vampire!"— ''Being escorted away to be tested on to unlock his memories all to help Shinoa"

- Chapter 77 "Rescue for the Devil", Page 1

"Mitsuba, I'll be fine. You go be there for Shinoa, okay?"— ''Reassuring Mitsuba just before Yu is struck with a needle and then kidnapped by the Hyakuya Sect."

- Chapter 77 "Rescue for the Devil", Page 22

"They say I hafta die! I'm not allowed to live! Everyone would be happier if I was dead! Because I'm demon spawn ..."

- In prison as a child, upset at what his parent's told him.

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

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

"I... I don't want to be alone. I don't ever want to feel this bad ever again. I... I just can't do any more than I already have. I wish I could disappear. Vanish forever!"

- After Mika does not come back, Yu processes the situation.

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

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

"This is super-duper bad! She was going to teach me how to save Mika! But now she's gone!"

- His reaction to Krul's brief absence and why he needs her

"I heard him! Just now! Mika is calling for me!"

- Alerting others that he can hear Mika, from the world he awoke in after being enveloped by an explosion.

"Mika needs helps! He's calling for me! And if he needs me, I'll go to him! Wherever he is! Anybody gets in my way an' I'll run 'em over!"

- Determined to help Mika.

"My Mika"

- About Mika

Trivia

 * The name Yūichirō means "excellence, superiority, gentleness" (優) (yū), "one" (一) (ichi) and "son" (郎) (rō), where 「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 four years where as livestock under the vampires he was not educated, Yu is nearly illiterate and only writes phonetically without using any Kanji.
 * Yu offers his blood three times before he finally convinces Mika to bite him in chapter 36 so the first vampire Yu is bitten by is Mika.
 * 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.
 * The past Yu in his life with Ashera it is shown that Yu already has Seraph powers as he grew angel wings behind his back.