Zero Kiryuu (錐生 零,
Kiryū Zero?) is one of the male protagonists of
Vampire Knight. Yuuki's close friend and the only other Cross Academy Guardian, Zero descends from a noted family of vampire hunters and was trained to be a Vampire Hunter by Toga Yagari. Zero carries an anti-vampire gun named "
Bloody Rose," given to him by Kaien Cross. His powers include accelerated healing, vampire detection, ability to withstand pure-blood compulsion and most recently the ability to manipulate vines within his body that are an extension of the Bloody Rose.
Four years ago, Zero was taken in by Kaien Cross as the sole survivor of a murderous attack on his family by Shizuka Hio. Zero was bitten during the attack and spent the last four years resisting turning into a vampire — the tattooed symbol on his neck helped suppress the vampire transformation. Due to the attack, Zero developed a deep hatred and distrust of vampires. He kept his vampire secret even from Yuuki until bloodlust overwhelmed him and he bit her. Filled with self-loathing, Zero attempts to run away but is stopped by Yuuki, who pledges to kill Zero should he fall to level E. To further ensure Zero's vampire nature remains controlled, the headmaster provides Yuuki with a bracelet that reacts with Zero's tattoo and paralyzes him
. Despite these measures, Zero's body rejects the blood tablets used to sate a vampire's thirst and Yuuki convinces Zero to continue drinking her blood. While Zero harbours romantic feelings for Yuuki, he supports her feelings for Kaname Kuran, in particular because Zero is gradually becoming a level E vampire. He is protective of Yuuki, preventing her from trading her humanity to Shizuka Hio in exchange for preventing his degenerating into a Level E vampire, swearing never to allow Yuuki to become a vampire; knowing this, Kaname Kuran allows Zero to live because Zero would do anything to protect Yuuki. However, with Shizuka's death, Zero is forced to drink the blood of a pureblood, Kaname, to delay becoming a level E vampire. Following Zero's discovery that Yuuki is actually a pureblood vampire, Zero and Yuuki sever their friendship, with Yuuki revealing that her vampire side "ate" her other side. Though Zero is able to maintain his sanity after drinking Kaname's blood, the Hunters Association arrange his arrest and lock him up. During this time, Kaname reveals that his purpose in strengthening Zero is in order for him to protect Yuuki and defeat Rido Kuran. Soon afterward, Zero is shot by his twin brother and finally completes the Twin Hunter fragment after he is convinced to "eat" the dying Ichiru. With this act, as a twin vampire hunter of an excellent lineage who has become a vampire and carrying the blood of three pure-bloods (Yuuki, Kaname and by proxy Shizuka
), Zero becomes one of the most powerful characters appearing in the series. Interrupting the battle between Yuuki and Rido, Zero declares his former friend his enemy, though they are able to work together and defeat Rido. Zero reveals his intention to kill all pure-blood vampires including Yuki, but finds that he cannot bring himself to kill her. Because of his own lingering attachment to her and as someone who made him feel safe, he finds such an act cruel and reveals that he would not mind if Yuuki killed him at that moment. However, when Kaname enters the scene, Zero does not hesitate to entangle him with the Bloody Rose, reasserting his desire to "exterminate all the pure-bloods." Zero realizes that Yuuki should be with Kaname. He tells her that he had craved for her blood only; vampire crave for the blood of the one they love, and he in effect confesses his feelings for her. He kisses her, and they separate. In the anime, the kiss does not happen; instead, Zero tells Yuuki to bite him in order to prove herself as a vampire, and she does so. As they part ways, Zero tells Yuuki he will find her and kill her, and Yuuki in turn says she will keep running from him so that he has a reason to live. A year later, he is still determined to kill all pure-bloods, but has decided to hold off on killing Kaname Kuran because it would jeopardize the peace. He appears to be indifferent towards Yuuki now, but his body still seems to lust for her blood.