Yūichirō Hyakuya/Relationships

Mother
When his mother's apartment goes up in flames, she screams that Yu is a demon and should die. She then dowses herself in gasoline and attempts to set herself on fire until firefighters tackle her to the ground. She succeeds in burning herself to death. Saito later reveals that she was not his biological mother however Yu is unaware of this.

Father
His father believes Yu should die for the good of the world, but ends up dead by Book 5 of Catastrophe.

Mikaela Hyakuya
Yūichirō's best friend and "family" since they were eight years old, Mika immediately welcomed Yu into their family when he was dropped off at the orphanage. Yu initially refused Mika's friendship and even challenged him to a fight which leads to him getting beaten by Mika. Even after that, Mika brings Yu into the family, and even relates to relates to his parental abuse. Then when the orphanage director dies and the vampires begin taking over, Mika had Yu look after the other orphans, and all of these events has lead to Yu to somewhat open up to his orphanage family. This comes off as him being the aloofness compared to Mika's friendliness. According to Yu, he would have died if it wasn't for Mika's kindness and friendship. which lead to Yu to not get close to others dedicate his life to kill them his "death" along with their family leads. Upon discovering Mika being alive, Yu becomes driven to save Mika, and even states that he'll promise to do so.

He wants to turn Mika back into a human and has convinced everyone in his squad plus Guren to help him take Mika from the vampires. Yu obsesses over Mika for the four years he believes Mika is dead. Although he hates vampires, Mika is the only exception. Yu claims the vampires are holding Mika hostage. He believes Ferid Bathory was the one to turn Mika into a vampire. He offered his blood to Mika in order for him to survive. In chapter 55 Mika holds Yu's hand to comfort him.

Akane Hyakuya
Part of Yu's orphanage family. She appears to be the mature and understanding motherly individual in the group, and she is the oldest out of the girls and third-oldest after Yu and Mika. Ferid Bathory kills her when they attempt to escape.

Mahiru Hīragi
She visits Yu while he is imprisoned and undergoing experimentation and asks him about the meaning of life. His memories are erased after the experiment. She later becomes the demon in Guren's sword.

Saitō
He saves Yu from his burning apartment and takes him to the Thousand Nights. He drags Yu to the orphanage Mika is at on Christmas Day, telling him he will meet people just as unwanted as he is.

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

Norito Goshi
One of Guren's squad members.

Sayuri Hanayori
One of Guren's squad members. Also Yu's teacher in the army classes.

Kureto Hīragi
The acting leader of the army and one of those involved with killing everyone in Nagoya.

Shinoa Hīragi
She joins the series as an army surveillance officer watching Yu. She becomes Yu's first female friend in the army, and he joins her squad later on. He eventually gets used to her teasing. Yu feels guitly once he becomes aware that he nearly killed Shinoa during his transformation on Shinjuku, He convinces her to help him save Mika. He saves Shinoa before Kureto kills her on Nagoya Airport. Over time, she develops a crush on Yu, but he has yet to realize her feelings.

Shinya Hīragi
One of Guren's squad members. He assists them in killing Lucal Wesker. Later on, he helps them escape Nagoya. A sniper.

Guren Ichinose
Yūichirō meets Guren when he reaches the outside world. Guren rescues him because he knows Yu is a survivor of the Hyakuya orphanage, and he wants to use Yu to reach his goals. After that, he becomes almost like a father to Yūichirō and teaches him how to survive in that world and use a sword. Even after learning that Guren is experimenting on him, Yu remains loyal to Guren. Yu convinces Guren to help him save Mika.

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

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

Mito Jūjō
One of Guren's squad members.

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

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

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

Aoi Sangū
Kureto Hiragi's aide. She is involved with killing everyone in Nagoya.

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

Yoichi Saotome
Yoichi is the first male friend Yu makes during his brief stint of high school. Yu helps Yoichi when he gets bullied. Later in that chapter, Yoichi tackles a vampire as she is about to kill Yu. Yoichi likes to hug Yu. Later, they both entered a squad under Shinoa. Like all his other comrades, he treats his friend nicely and is committed to saving him.

Shigure Yukimi
One of Guren's squad members.

Ferid Bathory
On their first meeting, Ferid asks for Yu, along with Mika to give him blood, but only Mika gives in. They meet for the second time when Yu and his family attempt to escape, and Ferid waits for them at the exit. Ferid slaughters their family in front of them. Although Yu managed to shoot Ferid in the head thanks to Mika's sacrifice, the injury is minor for a vampire. He believed Ferid was the one who turned Mika into a vampire. He has the gun Mika stole from Ferid prior to their escape attempt.

Chess Belle
One of Crowley Eusford's aides.

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

When Crowley surprises Shinoa Squad in the town near the sea, they surrender to him. He is laid-back and pities the children for getting involved in Ferid's schemes.

Horn Skuld
One of Crowley Eusford's aides.

Krul Tepes
Yu didn't meet Krul Tepes, however Mika explains him that Krul is the one who saved his life and she can be trusted, Yu shows simpathy about Krul since she gave Mika a second chance on living.

Lucal Wesker
The first noble vampire Shinoa Squad kills. They work in tandem with Narumi Squad and Shinya Hiragi.

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

Mirai Kimizuki
Shiho Kimizuki's sister and an awakened Seraph of the End. He fights her in his seraph form and wins.