Zero Kiryu

Zero Kiryu (錐生 零, Kiryū Zero?) is one of the main characters of Vampire Knight. Zero is Yuki's close friend and the only other Cross Academy Guardian. Zero carries an anti-vampire gun named "Bloody Rose," given to him by Kaien Cross.

Personality
As a child, Zero was a quiet and gentle boy, his twin, Ichiru questioned whether he was even capable of being a hunter. However after Shizuka's attack, Zero developed a deep hatred and distrust of vampires, he became withdrawn and sullen. He sports a scary aura that makes most of the day class students wary of him.

Background
Zero is descended from Vampire Hunters and was trained as a Vampire Hunter by Toga Yagari. Four years ago, Zero was taken in by Kaien Cross as the sole survivor of a murderous attack on his family by Shizuka Hiou. Zero was bitten during the attack and has spent the last four year resisting turning into a vampire. Zero was tattooed with a symbol on his neck that helped suppress the vampire awakening.

Plot Summary
Zero kept his vampire secret from Yuki until bloodlust overwhelmed him and he bit Yuki. Zero attempted to run away, stopped by Yuki, who pledged to kill Zero should he fall to level E. Following Zero's awakening as a vampire, his tattoo was used by Kaien Cross to allow Yuki to tame Zero. Zero's body rejected the blood tablets used to sate a vampire's thirst, thus Yuki convinced Zero to continue drinking her blood.

Zero harbored romantic feelings for Yuki, however he supported Yuki's feelings for Kaname Kuran. Zero prevented Yuki from becoming a vampire when attempting to trade for Shizuka's blood that would have saved Zero. He fought his master's compulsion and shot Shizuka to stop her biting Yuki. Zero swears he will never let Yuki become a vampire. Zero is prevented from drinking Shizuka's blood finding her already dead. In order to gain control and delay the fall into madness becoming a level E vampire, Zero was convinced to drink the blood of the pureblood, Kaname Kuran. Following Zero's discovery that Yuki is actually a pureblood vampire, Zero severed his friendship with her and likewise Yuki told him her vampire side "ate" her other side.

Though Zero regained his sanity, the Hunters Association have him locked up, arrested by Yagari. Kaname revealed that his purpose in strengthening Zero was in order for him to protect Yuki and defeat Rido Kuran. Zero is shot by his twin brother and finally completed the Twin Hunter fragment after he is convinced to "eat" the dying Ichiru. With this act, along with being a twin vampire hunter of excellent lineage who has become a vampire, within Zero is the blood of three purebloods, Yuki, Kaname and by proxy Shizuka, making Zero one of the most powerful characters in the series and saving him from becoming a Level E.

Zero's new powers are shown to be manipulation of vines within his body that are an extension of the Bloody Rose, which is capable of stopping Yuki's evolved Artemis Rod. Zero declared Yuki his enemy and attempted to keep her out of his fight with Rido. When Yuki struck the deadly blow to Rido's heart, Zero completed the destruction. Zero then turns the Bloody rose on Yuki and reveals his intention to kill all pureblood vampires including her.