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.

-Time Skip-

After the time skip of about one year Zero has been living off of Blood Tablets; after the incident of Yuki being awakened as her true self (being that she is a pure blood and Kaname's fiance); the the entire school being attacked by Vampires; and Zero "eating" his twin brother in order to gain his full power back. Zero has become a strong and very powerful being...even a great threat to the Pure Bloods. He continues to go to school (with reluctance), but cannot stay in the dorms due to him "hungering uncontrollably...by night" and hunts vampires at night to quench his thrust all the more on chapter 50. He can now control himself without Yuki's blood, but it is still difficult...His personality is still the same, but he still loathes the Pure Bloods to the point it makes him nearly insane.