Zero Kiryu's twin brother Ichiru Kiryu was, too, trained by Toga Yagari to be a Vampire Hunter like his parents. However, unlike Zero and his prodigal abilities, Ichiru was sickly and weak, which made Zero worry over him endlessly. One night, he overheard his parents saying that they did not know what to do with Ichiru because he was not suited to be a fighter, not like Zero. Though Zero loved his brother very much, Ichiru began to resent Zero and his parents. After hearing what his parents said, Ichiru ran outside and met a crying Shizuka Hio, who sat in a tree mourning her dead lover. In his pain, his confusion, and his anger, Ichiru connected with Shizuka.
After the death of his parents, Ichiru became a loyal servant to Shizuka and hid his survival from his brother. His hatred for Zero only festered, so much so that he tossed to Shizuka a sword with which to kill Zero. He still resents Zero for the fact that his parents did not hold him in the same regard as they did Zero.
According to the words of Kaname Kuran, twins from a Hunter family are extremely rare, even to a vampire that has lived for centuries. This is due to the fact that when Hunter fetuses are in the womb, they rely on instinct as they would in battle. This means that fetuses fight for supremacy and eat the weaker of the two. The fact that Zero and Ichiru were able to be born together is highly unlikely. There is evidence to suggest that the reason why Zero is more adept at vampire hunting and more healthy as a whole than Ichiru is because they were meant to be one, and Zero is simply the greater half. By one twin consuming the other, they become one, as they should have been in the first place.
Ichiru arrives at Cross Academy with Maria Kurenai, but does not reveal himself to Zero until 18th Night.
Shizuka starts laughing and tells Zero she will not die from those gun wounds. Zero pulls his arm from Yuki and starts shooting Shizuka. Shizuka blocks the bullets with strips of cloth from her kimono(?). Zero then tells that her he has been waiting for this day and decides to finish everything. Yuki once again stops him and Zero tells her to let go. Yuki lets go and asks him what will happen afterwards, but Shizuka interrupts with the answer that Zero has always desired to perish along with her. Zero again points the Bloody Rose to Shizuka, but out of nowhere, a katana (Japanese sword) is thrown and stabs Zero through the arm.
Zero is surprised and recognition dawns to him that his twin brother he thought was dead is alive. Ichiru Kiryu removes his mask and Yuki comments that he has the same face as Zero.
His revelation shocks Zero, but Ichiru believes that he knew all along. He expresses jealousy of Zero, because Shizuka refused to turn him into a vampire and shows too much interest in Zero.
After Shizuka is killed, Ichiru vanishes for a time.
In 25th Night, Zero senses Shizuka, looking around and finding Ichiru at the ball and begins to look for him. Zero noticed his younger brother and followed him as they talk briefly, who revealed that he became employed by the Senate after Shizuka’s death and working for the Vampire Company. Ichiru asks Zero if he has heard of the "Curse of the Hunter Twins." Zero became confused before Ichiru left.
Ichiru reappears as a student at the Academy in 30th Night. He is, of course, immediately popular in the school, a bright contrast to his gloomy twin. Ichiru makes disparaging remarks to Yuki about his brother's poor taste in women, to her embarrassment and later warns Zero not to fall in love with her.
Later, it is shown that, despite appearances, he is working for the council and aiding Rido Kuran, he is in fact seeking the healing of Rido, so that he can be fully killed. When his attempt goes awry, he seeks Zero once more and asks him to consume him, so that he can once more become a part of his brother. Ichiru's dying wish, though, is for Zero to live on and complete his goal.
When Yuki was leaving Cross Academy, she sadly watches Zero carry a now deceased Ichiru's body to be buried.
During the one year time-skip, Zero is seen visiting Ichiru's grave and he laments on how he fears he's forgetting how to feel like a human. Ichiru then appears as a spirit to comfort his depressed older brother. He calls Zero silly and to remember that his body may be within a grave with his parents, but his soul has become a part of Zero's so he remembers for him what it's like to be human. Lastly, he retells Zero to follow his heart before disappearing. When Yuki is drinking Zero's blood, she sees Ichiru within his memories along with the human version of herself standing beside a coffin covered by vines.
In the Manga
In the Anime
Ichiru arrives at Cross Academy with Maria Kurenai, but does not reveal himself to Zero until Episode 10.
Zero remembers telling his younger twin brother, Ichiru to flee after Shizuka’s attack.
Zero faces down Maria but can’t kill her. She says he can’t kill his master, who made him a vampire. She tries to kiss him, but he jerks back. She and Zero fight. Alarmed, Yuki calls his name, but Kaname puts her asleep. He erases Yuki's memory of that night, saying that he cannot lose Yuki but that Zero can die if he’s that weak. Zero faints from an injury, and Maria tells her bodyguard to carry him away.
Meanwhile, Zero dreams of Shizuka and Ichiru. Zero recalls as a child that he and Ichiru discreetly meeting Shizuka. Upon first seeing her, Ichiru finds her beautiful but Zero sensed that she’s a vampire during the day. Ichiru says that Zero's amazing and makes up for Ichiru's mediocrity. That night, Ichiru asks if the vampire they saw earlier will be killed and if kindly Zero will be able to hunt vampires. Zero says Master will teach him to. When Shizuka suddenly appeared at night and attacked Kiryus, out of revenge for killing her lover. Zero sees Ichiru standing next to Shizuka, smiling. Zero wakes up and sees Maria's bodyguard, he coldly greets him and told him to take off the mask, who he knows is his twin brother. The bodyguard removes his mask to reveal himself to be Ichiru.
Zero faces Ichiru, who reveals his past feelings of envy and worthlessness and how he and Shizuka became allies. Ichiru tells Zero that even though he wants to kill Zero, he won’t if Zero serves Shizuka. Zero apologizes for getting Ichiru turned into a vampire. Angry, Ichiru attacks. Zero blocks it but keels over, overcome by blood thirst.
Toga bursts through the door to retrieve Zero. Ichiru challenges him, but Toga refuses to fight, saying that Ichiru was his disciple. Angry, Ichiru draws his sword. Zero steps in to defend his teacher. Ichiru is knocked over by Zero’s strength and his sword flies through the air. It falls straight for his throat, but Toga takes the blade in his shoulder, shielding Ichiru. Zero brings Toga to Headmaster Cross and departs. Toga tells Cross that Ichiru is back and asks if Cross still plans to not interfere.
Zero shoots his own leg and the pain breaks his compulsion. He wounds Shizuka with the Bloody Rose. Zero again points the Bloody Rose to Shizuka again but Ichiru enters, throwing his sword into Zero's firing arm. While Zero is pulling out the sword, Shizuka tells Ichiru not to meddle and leaves. Zero tries to go after Shizuka but Ichiru blocks him and tells him is he playing on leaving again. Zero angrily says to Ichiru that he was the one who left, who meant the vampire world.
Yuki asks Zero who Ichiru is. Ichiru says to Zero isn't he going to introduce them. Zero tore the mask off of Ichiru and says to Yuki that he's his twin brother. Yuki became surprised that Ichiru has the same face as Zero.
Ichiru pulls out a dagger and begins fighting with Zero. Then, Yuki jumps between them and say they shouldn't as they are brothers, and Ichiru threatens to kill Yuki against Shizuka's orders. Zero retaliates by pressing his gun to Ichiru's head, but Ichiru reveals that it won’t work on him because he’s still human. Zero lowers his gun and says he knew it. Ichiru becomes enraged, explaining that although Shizuka gives him her blood, she doesn't want his in return. He loves her, but like their parents, Shizuka seems to prefer Zero over him. Ichiru pushes Yuki out of the way to attack Zero.
All the vampires smell blood. Zero tells Ichiru that the smell of blood is strong and Ichiru realizes that it’s Shizuka's. He leaves to find her. Zero tries following but Yuki hugs him and says she doesn't want him to perish with Shizuka as he planned. He pushes her away gently and says it’s different now, he will come back. Ichiru has already reached Shizuka and finds her dying on the floor.
Zero rushes into the room and finds Shizuka and Ichiru as Ichiru is licking the remains of something from his lips. Shizuka’s corpse dissolves into the air. Meanwhile, the puddles of her blood everywhere have stimulated Zero’s level E impulses and he collapses. Ichiru relates the hatred Zero feels for him. Zero tells him that Shizuka wanted you to stay the way you are not a vampire. Ichiru taunts him. Zero calls out to Ichiru but he disappears.
Meanwhile, Zero has been assigned to oversee the party by the Hunter's Association. Zero senses Shizuka, looking around and finding Ichiru at the ball and begins to look for him. Zero noticed his younger brother and followed him as they talk briefly, who revealed that he became employed by the Senate after Shizuka’s death and working for the Vampire Company. Ichiru asks Zero if he has heard of the "Curse of the Hunter Twins." Zero became confused before Ichiru left.
Zero talks to Kaien about the "Curse of the Hunter Twins" when Ichiru asked him about it.
Ichiru applies to the Day Class and the Headmaster accepts him after he gets approval from Zero. The Headmaster hopes that the brothers will be able to come to an understanding of one another someday and is proud of Zero for acting so maturely. Ichiru is charismatic and quickly becomes popular among the students, a stark contrast to his older brother. When Zero enters the classroom, he and Ichiru talk alone for awhile outside before Ichiru walks away. After a talk with Zero about his courage to face his brother, Yuki resolves to talk to Kaname once more about her past.
When Yuki collapses from these images, she is taken to the infirmary, where Ichiru attempts to give her a vial of blood, and he suddenly has visions of Shizuka and Zero then is stopped by Hanabusa, who takes the vial.
Yuki and Headmaster Cross try to invite Ichiru to dinner in an attempt to have Zero and Ichiru reconcile their differences. However, Yuki brings up that she saw Ichiru in the infirmary and thought he was Zero. Zero's furious response to this causes Ichiru to leave. He tells Kaien that it's too late to choose a different path. Later Ichiru tells Zero not to fall in love with Yuki.
Zero notices Ichiru with 'Senri'.
Meanwhile, Kaname goes to where Rido is being kept and finds Ichiru there. As Ichiru opens the coffin, Kaname tells him that usually, hunter twins will kill their sibling while still in the womb, and that Ichiru is the first he has met to have been born with his twin and Zero was kind-hearted before he was even born. Ichiru arrives in the prison cell and shoots Zero with the Bloody Rose he picked up, wounding him. Zero recalls the close and loving relationship he had with Ichiru when they were children and remembers Shizuka killing his parents. Ichiru, revealing that he was injured while attempting to kill Rido for Shizuka's sake because it was Rido, who was the one who put her lover on the list. Ichiru asks Zero to consume his blood so that they can "become one". Ichiru is happy when Zero says he doesn't wish for Ichiru to die as he still had some love for his little brother and that Maria wishes to see him. Pretending to die from his wound, Ichiru succeeds in making Zero consume his blood so Zero can complete his vampire hunter powers to control his thirst for blood. Zero leaves the bell Ichiru kept as a memento of Shizuka in his brother's hand before leaving the prison cell.
Zero stops convulsing and feels that the pain he is feeling is proof he and Ichiru have become one. Grabbing his Bloody Rose, Zero points it at Rido as the weapon begins glowing. Rido invites him to kill him as many times as he likes as he'll keep coming back.
- Ichiru's favorite food is anything Zero makes.
- As Kaname notes, kindness is a trait Zero had even before he was born. Ichiru was the weaker twin, and should have been consumed by Zero; however, Zero did not, just a sign of how kind he can be.
- Ichiru's hobbies are things concerning Zero.
- Ichiru's Favorite Fashion: Anything Zero or Shizuka-sama chooses for him.
- "Ichiru told me to live... and fulfill my goal. But I was afraid..All this time...I haven't faced my true feelings. I won't hide behind excuses anymore." (Zero to Yuki)