Yūichirō Hyakuya/Relationships

Mikaela Hyakuya
He is Yūichirō's best friend, and "family" that saved him from being killed. Mika was the reason why Yuichiro hated vampires and had dedicated himself to kill them after the death of his family. It's shown in chapter 14 that Yuichiro still wishes 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.

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.

Lieutenant Colonel 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.

Sergeant 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. He convinces her to help him save Mika. Over time, she develops a crush on Yu, but he has yet to realize her feelings.

Second Lieutenant Mitsuba Sangu
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.

Special Private 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.

Special Private 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 Shiho as a comrade who he'd protect and a family member of their group.

Seventh Progenitor 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 believes Ferid is the one who turned Mika into a vampire. He has the gun Mika stole from Ferid prior to their escape attempt.

Thirteenth Progenitor 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.

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.