Personality

As a child, Zero was a quiet and gentle boy, to the limit where Ichiru questioned whether or not he was even capable of being a vampire hunter. However after Shizuka's attack, Zero developed a strong distrust of vampires. Zero is a tsundere character, he sports a scary aura that makes most of the Day Class students wary of him, he can also glare in a way that even Kaname Kuran calls it scary. However, his innate nature is to protect humans, his cold attitude towards those he loves is likely to push them away and keep everyone at a distance. He also happens to be a stickler for details, as he doesn't consider himself as an adopted son of Kaien's family with Yuki, or holds all the details about how vampires and humans can be similar in their own ways. As told by Ichiru to Kaien, Zero's favorite food is vegetable soup.
Following his full awakening into a vampire, Zero harbors a great disgust towards himself because of inability to control his hunger and reliance on Yuki. His dismal outlook on his future and fear of what he might do causes him to give up and he almost kills himself with his anti-vampire gun, The Bloody Rose. He ignores his hunger to the point of starvation rather than go to Yuki. He tries to help Yuki resolve her own problems and then impresses upon her that its alright for her to burden and use him because she owns him.

Zero is hostile to the Night Class vampires when they threaten him, however he adopts his standard tsundere attitude when engaging them one on one retaining a level of civility. Zero expresses a great deal of anger toward Purebloods because of their mechanisms in his life in particular, he extends this hostility toward Yuki as well after she turns into a Pureblood vampire. In spite of this, his sense of duty overrides his issues ensuring his reliability and trustworthiness.