Zero Kiryu

Zero Kiryu is Yuki Cross childhood best friend. Zero is also a Cross Academy Guardian and likewise on the disciplinary committee.

Background
Yuuki has cared about him as a close friend ever since he was brought into their home (the Headmaster's). His family, one of vampire hunters, was murdered by the pureblood vampire Shizuka Hiou when he was young. He harbors a deep hatred for vampires and claims to have taken on the role of Guardian to learn how to hunt them better. In truth, Zero was bitten during the attack on his family and therefore was turned into a vampire, something that has been kept secret even from Yuki until his vampiric urges began to surface and became uncontrollable. As Zero's body rejects the blood tablets that most vampires take to control their hunger, Yuuki began letting him drink her own blood, which helps his thirst for blood, but he is ultimately to become a Level E vampire. The story implies that Zero harbours romantic feelings for Yuuki. In chapter 35, he discovers Yuuki is a vampire, and in chapter 37 he aims his gun at her, which leads to Yuuki telling him her vampire side "ate" her other side. He almost kissed Yuuki twice showing that he has feelings for her.

Zero is currently being locked up by the Hunters Association. In chapter 39, it is implied that Zero might be a significant person who is crucial to the defeat of Kaname and Yuki's nemesis. As Kaname said himself, Zero is a vampire hunter with an excellent lineage being at the same time a vampire himself. And thanks to having taken blood of three purebloods, Yuki, Kaname, and Shizuka

Triva

 * Voiced by: Mamoru Miyano in the japaness anime