Yuuki's childhood friend, Zero is also a Guardian and likewise on the disciplinary committee. Yuuki has been taking care of him as her little brother since he was brought into their home (the Headmaster's). His family, a line of vampire hunters, was murdered by the pure blood vampire Shizuka Hio when he was young. He harbors a deep hatred for vampires and claims to have taken on the role of Guardian to learn to hunt them better. In truth, Zero was bitten during the attack on his family, and have kept the secret that he was a vampire from Yuuki until he was no longer capable of controlling his vampiric urges.
Zero's body rejects the blood tablets that most vampires take to control their hunger. Drinking Yuuki's blood helps him maintain his sanity, but he is destined to become a Level E vampire eventually. He has started to accept his feelings towards Yuki and has gone as far as to almost kiss her. Zero's weapon is the gun "Bloody Rose," given to him by Headmaster Cross. He made Yuuki promise that if he becomes a Level E vampire, she will kill him with that gun