Zero Kiryu (錐生 零, Kiryū Zero?) is unique being both a Vampire Hunter and a vampire. Yuki's close friend and a Cross Academy Guardian, he was trained to be a Vampire Hunter by Toga Yagari. Zero carries "Bloody Rose”, an anti-vampire gun. On one side of his gun it says "Crossing" and on the other "Bloody rose". On the front of the gun below the opening in the barrel you see a symbol, that is the same symbol the gun shoots to kill the vampires. Zero lives with Kaien Cross and Yuki, after being bitten by a Pureblood vampire who also murdered his family. Due to the attack, Zero developed a deep hatred and distrust of vampires, despite originally being a gentle character by nature; however, he retains his kindness beneath his scowls, always looking out for the Day Students in case the Night Class "misbehaves". He has a tattoo on his neck that allows him to be restrained by a charm that temporarily embolizes him and allows him to enter the Hunter Society's headquarters. Zero also holds a deep hatred for Kaname Kuran, who tells him that he is simply a shield for Yuki. Zero is deeply in love with Yuki, but chooses to hide it; his feelings with left temporarily confused after Yuki was revealed to be a Pureblood vampire, but Zero continued to love her. In the anime's final episode, Zero lets her drink his blood, allowing Yuki to see how he feels about her. He is one of the few vampires whose body refuses blood tablets, leaving him constantly thirsty for blood; Yuki oftens gives him her blood to satisfy his thirst. A funny fact is that Zero doesn't care what kind of outfits he wears, often leading Yuki to shop for him. After the time skip, Zero is being considered for the position of the Hunter Society president; he also drinks the blood of vampires he hunts to satify his thirst. Matsuri Hino described Zero as exemplifying her hesitant nature.

After Kaname sacrifices his heart to restart the creation of Anti-vampire weapons, Zero confesses to Yuki so they can start a relationship. They have a son and daughter, the latter however is left ambiguous whether she belongs to Zero or Kaname. They live together happily for years until Zero passes away.