Zero was born into the Kiryu family, a prestigious vampire hunter bloodline, alongside his younger twin brother, Ichiru Kiryu. The two shared a close bond in childhood, but their destinies would soon diverge due to tragic events.

When Zero was a child, his entire family was slaughtered by the Pureblood vampire Shizuka Hio, who attacked in revenge for the hunters killing her lover. Zero survived but was bitten by Shizuka, an act that cursed him to turn into a vampire something he despised more than anything.

Following the massacre, Zero was taken in by Kaien Cross, the headmaster of Cross Academy, where he was raised alongside Yuki Cross. He kept his vampire nature hidden and worked as a Guardian of Cross Academy, tasked with protecting humans from vampires while battling his own bloodlust and self-hatred.

Zero has silver hair and striking lavender eyes, which are a trademark of the Kiryu bloodline. His pale complexion and sharp facial features contribute to his cold and brooding appearance.

As a student and Guardian of Cross Academy, Zero wears the white Day Class uniform but often accessorizes with a black choker and gloves to hide his hunter tattoo, which is used to suppress his vampiric urges.

After fully embracing his role as a vampire hunter, Zero adopts a more mature and battle-ready look, often seen in hunter attire, emphasizing his transformation into one of the most powerful hunters in history.

Zero is stoic, cold, and fiercely independent, often keeping his emotions hidden. Due to his traumatic past, he develops an intense hatred for vampires, seeing them as monstrous creatures who destroy lives. However, beneath his hardened exterior, Zero has a strong moral compass and deep capacity for love, even if he rarely expresses it.

Initially, Zero keeps everyone at a distance, refusing to open up about his pain and suffering. However, as the series progresses, he gradually softens, especially towards Yuki, who becomes his anchor and closest companion.

After Yuki is revealed to be a Pureblood vampire, Zero is deeply conflicted, torn between his love for her and his ingrained hatred for vampires. This internal struggle is central to his character arc, as he slowly learns to accept his fate and emotions.

Despite his tragic circumstances, Zero remains determined and resilient, ultimately choosing to fight for justice rather than giving in to vengeance.

• Guardian of Cross Academy
  At the start of the series, Zero is a Guardian of Cross Academy, responsible for maintaining peace between the Day Class and the Night Class. Alongside Yuki, he ensures that the existence of vampires remains a secret while suppressing his own bloodlust. Though he acts indifferent, Zero often protects Yuki at all costs, even risking his life multiple times. His deepening bond with her is one of the driving forces of the story.

• Struggle Against His Vampire Nature
  As Zero’s hunger for blood intensifies, he begins to lose control over himself, leading him to rely on Yuki to survive. Despite his hatred for vampires, he is forced to drink Yuki’s blood, creating a complicated relationship where she becomes his lifeline and greatest temptation. His inner turmoil worsens when he learns about Kaname Kuran’s true connection to Yuki, further deepening his resentment and rivalry with Kaname.

• Rise as a Vampire Hunter
  After Kaname kills Rido Kuran, Zero is granted the full power of a vampire hunter, inheriting the Bloody Rose, a powerful anti-vampire weapon. He becomes one of the strongest vampire hunters, eventually leading the Hunter Association after the death of its corrupt leaders. As tensions between humans and vampires escalate, Zero struggles with his role as both a hunter and a vampire, walking the thin line between justice and vengeance.

• Yuki’s Departure and Reunion
  Zero is devastated when Yuki leaves Cross Academy with Kaname, believing that she has chosen her vampire heritage over him. Though he initially tries to bury his feelings, his love for Yuki never fades. Years later, the two reunite under tragic circumstances, as they find themselves on opposite sides of the growing conflict between vampires and hunters. However, their bond remains unbreakable, and they ultimately reconcile, choosing to fight together for peace. In the end, after Kaname’s sacrifice, Zero and Yuki share several happy years together, during which Yuki gives birth to Ren Kiryu, their daughter.