Yūichirō Hyakuya

Yūichirō Hyakuya 「百夜 優一郎, Hyakuya Yūichirō」 is a member of Japanese Imperial Demon Army's Moon Demon Squad and is the main protagonist of the Owari no Seraph series.

Appearance
Yūichirō has medium length black hair which can be considered quite messy. He possesses sharp green eyes which fall under his thick eyebrows, His eyes are large compared to most other male characters in the series. At the beginning of the series, he is often shown wearing a typical Japanese school uniform with a white sleeved T-shirt beneath.

After joining the Imperial Demon Army, he takes on their uniform consisting of a black jacket with light green details, and dark gray trousers and black boots which go over his trouser leggings. Yūichirō keeps his sheath on the left side of his hip. Sometimes he can be seen wearing the Japanese Imperial Demon Army hat. He often wears the JIDA cape as well.

Personality
He is brave, fearless and somewhat reckless, which is shown in the beginning of chapter 2 when he attacks a Four Horsemen of John while ignoring orders. It is noted not to be the first time. Yu is often called an idiot by those who know him. He is a very narrow-minded person, whose goal is to annihilate all of the vampires because of what they did to his "family," and he will overcome any type of challenge in order to accomplish it. He swears to kill all vampires because they killed Mika.

Despite this, he has a soft spot and worries about his friends first and his goals second. Some (mostly vampires) consider his personality as 'cute,' such as Ferid Bathory. Also he empathizes with others who put their family first, as seen when a civilian girl gave them 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 is obsessed with Mika, having nightmares about Mika's death repeatedly for the four years until he makes friends with Shinoa and Yoichi. After learning Mika is alive, Yūichirō'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. His dream of genocide takes second place to reclaiming Mika. Even though his best friend is now a vampire, Yu still slaughters them without mercy or hesitation. He becomes closer to his squad members and Guren as well, making them promise to help him take Mika back. Friendship and bonds become more important to him. While in a mental battle against Asuramaru to gain more power or else lose his body to Asuramaru, he even 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; in contrast, he cannot even recall the name of their vampire target.

History
Yūichirō Amane was born in 2004.

During his childhood, both of his parents screamed that he was demon spawn. Yūichirō's father and possibly mother tried to kill him. His father screamed that he had to kill the seraph of the end now or else the world would be ruined. His mother went mad and committed suicide, and Yu's home went up in flames.

This lead to Yu being taken to the Hyakuya Orphanage in Tokyo while being told he could meet friends who were just as unwanted as he was. This was on Christmas in 2012. He met Mikaela and the other orphans. Seeing as the two 8-year-olds were the eldest,  Mikaela wanted them to be friends, but Yu rejected him. Mika asked if Yu were challenging him to a fight and said he was the leader. They fought, and Mika gave him a serious smack-down. Afterwards, he told Yūichirō that he used to be alone like him, but now he had a big family. And from that day onward, Yu had one too. Yūichirō 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. Mikaela then told Yūichirō 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 lead 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.

After Mikaela steals a gun and a map of the underground, they made a daring escape attempt with their orphanage family. Unfortunately, this was all a trap set by a seventh progenitor named Ferid Bathory, who had relations with Mika. Ferid slaughtered the other children in front of Yu and Mika. Yu managed to shoot Ferid in the head, but Mika was fatally wounded. Yu called Mika "family" for the first time. He refused to leave Mika behind until Mika yelled at him and pushed him away. Yu escaped, leaving Mika behind; this action haunted 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 finds 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 was 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 joined the Japanese Imperial Demon Army as Yuichiro Hyakuya.

Story
Guren agrees to give Yu the power to kill vampires when they first meet, but he does not put Yu in a vampire extermination unit right away. Four years later, Yūichirō is a private of the Japanese Imperial Demon Army. He gets suspended from the army for disobeying orders and is forced to attend Shibuya High School #2 in the meantime. When Shinoa tells him his suspension will continue until he makes friends, Yūichirō struggles since he has stubbornly rejected forming close relationships since Ferid Bathory slaughtered his family. He insists he does not need any friends. 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. Yoichi tells him he wants to join the army to get revenge for his sister's death, but Yu tells him to forget the army and that his sister wouldn't want him to avenge her death. An emergency warning goes off, and Yu challenges the escaped vampire assailant, nearly killing her when Guren arrives and ends her life. Yoichi becomes Yu's friend, meaning that Yu actually reached the requirement Guren gave him. In a dream, Yu's orphanage family tells him farewell.

IIn chapter 3, Yu learns that Shinoa has a demon weapon for slaying vampires and wants to take it from her by force. She rapidly relieves him of that notion. Yu, Shinoa, and Yoichi save Yamanaka's friend Yuji. 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.

IIn chapter 4, Yu meets and fights with Shiho 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.

Natural Abilities
Yūichirō seems to be a excellent swordsman, as he was trained by Glen himself. This is shown when he killed a Horseman of the John using only a sword.

Demon Weapon

 * Asuramaru 「阿修羅丸」: Asuramaru is a demon of the Black Demon series. It resides inside a black sword that Yūichirō uses. Whilst in use, the blade develops a thick green aura. Like Shinoa Hīragi, he can call upon Asuramaru to fully use its power to attack opponents. His type is possession.

Trivia

 * It has been confirmed that he has part of him that is inhuman.
 * Since he lived in a vampire city for 4 years, he was able to learn to read and write in English.
 * Yūichirō means "Superior First Son".
 * Hyakuya means "Hundred Nights".

Quotes

 * 'If Mika needs me... If Guren, Shinoa, Yoichi and Kimizuki need me, I don't care if I'm a devil or anything.' - Yūichirō to Asuramaru in The Demon's Nightmare.