Yūichirō Hyakuya/Relationships

Step-mother
When his step-mother's apartment goes up in flames, she screams that Yu is a demon and should die. She then douses 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, but was his step-mother, however Yu is unaware of this.

Father
His father believes Yu should die for the good of the world, is willing to stab and kill him to achieve this goal, but ends up dead before being able to. This experience had affected Yu, as he cries about it to Mahiru while being held captive by the Hyakuya Sect. Asuramaru later uses this memory to terrorize him in a nightmare.

Mikaela Hyakuya
Mikaela Hyakuya is Yūichirō's best friend and "family" since they were eight years old. Yu calls Mika by his shortened nickname, "Mika". 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 lead to him getting beaten by Mika. Even after that, Mika brought Yu into the family, and even related his parental abuse.

After the virus killed the orphanage director and the vampires took custody of the Hyakuya Orphans, Mika and Yu looked after the younger orphans, eventually creating Yu's "family." Yu and Mika once discussed what they would do if they left the vampires' city, Yu saying that he would like to go to paradise and Mika then smiling and saying that he should work hard, leaving Yu confused. Later, it reveals that Mika had been going into the 7th Progenitor's (Ferid Bathory's) home to offer his blood in order to steal a map and gun to escape.

Mika convinced Yu and the rest of the orphanage children to come with him to escape the city through the Ferid Bathory's house, but is killed while doing so. Yu was the only survivor and was haunted by his family due to him running away after they were slaughtered.

It turned out that Yu was, in fact, not the only survivor, when Queen Krul saved and converted him into a vampire. However, he refused to become a complete vampire and subsisted on Krul's blood to keep his thirst at bay.

After Yu joined the Moon Demon Company, he met Mika once more after he tried to kill him from behind after discovering that a vampire wanted to take one of his comrades. However, when he realized that it was Mika he stabbed, he pulled out immediately and was in complete shock and confusion. After realizing that Mika was converted, he retreated back with the Moon Demon Company and searched for ways to turn a vampire back into a human.

Mika saw Yu once more on the battlefield after forcing information out of a soldier (Aiko Aihara) about Yu's location. However, he spotted Yu unconscious after his battle with Crowley, and thought it to be the humans' doing. He immediately rushed ahead to take Yu from his group, but got severely injured while doing so. When he was about to die, the Shinoa Squad squad defended him while he took Yu away.

After Yu woke up, he saw how thirsty Mika was even after Krul's blood, and encouraged him to drink his own. Mika put up a fight against it, protesting all the way through, but he gave up after Yu claimed that he could not live if he watched his family die once more. After he finally drank Yu's blood, his eyes turned from blue to red, signaling that he has finally become a true vampire.

Mika's seemingly only reason to live was Yu, and would go to any depths to protect him, even if it meant holding a sword to his throat. Yu felt the same about Mika, but had a larger family he must protect and begged Mika to accept his new family.

Akane Hyakuya
As children, Yu was not the kindest to her, and denied when she said that they're all apart of the same family. When she died, Yu was very saddened over her death along with Mika and the other orphans. He was completely enraged and even started to go berserk with his demon once Ferid showed him her decapitated head in a jar. Later in Ferid's mansion, before going downstairs to see the encased corpses of his family, Yu told Yoichi he'll carry Akane's head. Once given to him, he then apologized to her for never calling her "family" and running away. At Guren's mansion, he says that once he brings back Akane and the other children, he says next time, he'll say they are family.

Mahiru Hīragi
Mahiru visits Yu while he is imprisoned and asks him about the meaning of life. Yu at first tells her to go away, but she does not. When Yu tells her that he is a demon spawn, Mahiru questions why he thinks that, and says he appeared human to her. Before the researchers mess with his memories, she tells Yu to stay strong and that one day, she will return to free him from the Hyakuya Sect. Eight years later, after Asuramaru finds this memory deep in his mind, Yu tells Guren that he vaguely remembers her but not her identity.

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.

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. After the battle in Shinjuku, Shinoa starts to develop a crush on Yu, but he has yet to realize her feelings. He is able to convince her to help him save Mika, and they hold hands. Yu shows guilt once he learns that he nearly killed Shinoa during his transformation at Shinjuku. He saves Shinoa before Kureto kills her on Nagoya Airport. Shikama Doji later reveals to Yu that she is in love with him and tries to save her from his grasp, ignoring Asuramaru's warning. He is devastated after seeing her in a comatose state to the point of ignoring his status as a former soldier and being experimented on by Kureto's order, as long as Shinoa is saved.

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, 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.

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.

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. He is not aware of her feelings for him.

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. When Crowley captures Guren, Yu gets angry and disobeys orders to save him from the vampire. He acquired his whereabouts through Mahiru connection with Saito at the Hyakuya Sect.

Sayuri Hanayori
One of Guren's Squad members.

Shigure Yukimi
One of Guren's Squad members.

Norito Goshi
One of Guren's Squad members.

Mito Jūjō
One of Guren's Squad members.

Shinya Hīragi
One of Guren's squad members. He is made to battle him when Kureto suspects a traitor amongst them. He assists them in killing Lucal Wesker. Later on, he helps them escape Nagoya. A sniper.

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.

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

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

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

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

Kureto Hīragi
The acting leader of the army and one of those involved with killing everyone in Nagoya. After learning he is the 2nd Trumpet The King of Salt he orders his soldiers to capture him.

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

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. Ferid is easily the vampire he resents the most for his massacre of his family-like friends, as shown by how he is the only Vampire Yu remembers and when they meet, he gets agitated and ferociously attacks him.

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 sympathy about Krul since she gave Mika a second chance on living. She later discovers that her brother Ashera is in Yu cursed gear after sensing him.

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. He was Mahiru Hiragi's former weapon, and following her death, he becomes Yu's cursed gear after he makes a contract with him. Until Yu weakens the curse binding, Asuramaru 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 in Nagoya, Yu is chained to a wall, and appears with fangs and horns with the wish of getting free. Asuramaru seems to have complete control over Yu's body.

When Yu tries to talk about Asuramaru memories he notes that every time his angel is out of control and his body and heart gets destroyed, he starts regaining little by little his memories, he says he has a feeling that he have a sister whom he regrets abandoning and falls asleep from the headache by remembering. After the Hyakuya Sect captures Yu, in his mind he's has been struck by two long spears weapons, while Asuramaru in front of him he suddenly finds it odd for his memories to be returning.

During the Dark Ages of Greece, when Ashera was a human, Sika Madu brought a slave named Yu to free the imprisoned Ashera. He tried to befriend Ashera, such as promoting him playing with him. However, Ashera was not interested but promised him that he will play with him someday if he got used to his situation. Ashera was not aware that Yu possessed seraph powers at that time, as the latter was astonished when he saw angel wings appear behind his back.

Shikama Dōji
Shikama Doji seems to be familiar with Yu, as after seeing him in Asuramaru's mind Shikama Doji tells him its been a long time since he last saw him. Prior to becoming the demon Shikama Doji, Sika Madu buys a slave named Yu with him to free the imprisoned Ashera and later tries to befriend Ashera, he used to obey every Sika Madu orders, having been with him for a long time likewise Sika Madu is fond of Yu and shows interest in him for unknown reasons. It is later revealed that Sika Madu only uses Yu such as the case when he used Yu's blood to turn Ashera into a vampire. He has no qualms of discarding him if he deems useless but Sika Madu kept Yu due to his blood compatible with Ashera which he takes interest in.

Later on Shikama Doji invades Asuramaru's heart and Yu comes to the rescue. Seeing both Asuramaru and Yu are in good terms he is delighted he also tempts Yu about his past as he known him for a very long time despite Yu's denial. He defeats Shikama Doji seemingly. telling Yu that he was just supposed to be another empty vessel. Yu wonders who he is as he knew his past.

Noya
In the Dark Ages of Greece Noya seems to know quite a lot about him. Though appeared cautious as the young Yu approaches the corpse of "Mikaela", taking interest in it, Noya tells him he could call it a fun toy and, Noya helps him see what is in the coffin before killing Yu. Noya did this believing it would save him, Ashera and Krul and it's not a problem as Sika Madu will create more Yu's anyway. In the present, upon seeing a fully grown Yu. Noya is surprised..

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

6th Trumpet
An Angel whom Yu fights and wishes to save him despite the 6th Trumpet have no desire to listen to him, Yu keeps fighting him together with Asuramaru whom he discovers he also has a demon inside, eventually Yu and Kimizuki were able to stop him by pinning him down and inject him with a drug and now appearing as a human.This also this puts an end to the Horsemen of the Apocalypse.