Zero Kiryu

Zero Kiryuu (錐生 ゼロ, Kiryū Zero) is one of the main characters of Vampire Knight. Zero is Yuki's childhood friend and the only other Cross Academy Guardian. Zero carries an anti-vampire gun named "Bloody Rose". Zero is the only Vampire Hunter/vampire who appears in the story.

Character outline
Even before becoming a vampire, Zero was noted to be a talented vampire hunter due to being the stronger of a pair of rare twin hunters. Zero bears a tattoo on the left side of his neck originally used to supress his vampire side, later used to tame him. Zero is a casual dresser, usually wearing school uniform incorrectly with the vest and red tie exposed from under his black jacket and wears a fang like earing. Zero was born in the year of the Dog and is 181cm (5'11) in height.

Personality
As a child, Zero was a quiet and gentle boy, to the point where Ichiru questioned whether he was even capable of being a 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. 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.

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. He fights to ignore 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 very hostile to the Night Class vampires when they threaten him, however he adopts his standard tsundere attitude when engaging them one on one while retaining a level of politeness. 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. In spite of this, his sense of duty override his issues ensuring his reliability and trustworthiness.

Background
Zero was born in a vampire hunter's family and had a identical twin brother named Ichiru. They, along with Kaito Takamiya, were trained as vampire hunters by Toga Yagari. Kaien later comments that they share a similar line of thinking thanks to this. Yagari lost an eye protecting Zero, when the still naive Zero makes himself vulnerable to ex-human vampire when the nurse turned wild and tried attacking Zero due to her Level E state. This was Zero's first lesson on the dangerousness of seemingly innocent vampires.

Ichiru and Zero were once very close. Due to Ichiru's frail body, he could not keep up with training and lacks the essential skills. Ichiru constantly got sick, causing Zero to feel guilty about sharing their mother's love. One day Zero and Ichiru were taking a walk and Ichiru saw a women sitting in a tree. Ichiru was in awe of how pretty she was, but Zero told Ichiru that it was a vampire and told him to stay away from her. A few days later, Ichiru ran off and Zero sense the approach of the pureblood vampire and ran to confront her. That vampire took Zero and bit him, hence turning him into a vampire. His parents came out in an attempt to save Zero but were killed, Zero at the time also believed his brother was killed.

After that attack Zero was taken in by Kaien Cross, the headmaster of Cross academy. His temperament turned cold and hostile, at times cruel to the young Yuki who reached out to him. Her gentleness won him over, but Zero kept his affection for her to himself, aware that she loved a vampire. However, Zero failed to reveal that he was going to turn into a vampire after Yuki revealed she was afraid of all other vampires. Over the next four years, the two became friends and Zero became her constant protector while Yuki mothered him.

Ichiru Kiryu
Zero &amp; Ichiru

Zero's twin brother. In Zero's childhood, he and Ichiru have been very close siblings. It all came to a halt when Ichiru spotted Shizuka, a Pureblood who thought the Kiryu family killed her human lover. Worse news came to Ichiru when he heard his parents preferred Zero over him. When Shizuka slaughtered their parents, Zero instantly told Ichiru to run away, showing how much he cared for his twin. Soon after that, Zero went on to be with the Cross family: Kaien and Yuuki at the age of twelve years old. When Zero was locked up by the Vampire Hunters Association, Ichiru visits him and appears to have shot him due to hatred. However, it is revealed that Ichiru was terribly wounded because he tried to kill Rido, the person he was truly after because of his role in Shizuka's death. After he shoots his brother, he convinces Zero to drink his blood so they could finally become one as they were originally supposed to be. Ichiru stated that he was happy that he was not dead in Zero's heart and when they hug, he says that he feels comfortable to be in his arms, recalling a time when the brother's slept in the same bed often and were loved equally by their mother.After Ichiru's death, Zero appeared to grow vines, most likely from all of Shizuka Hio's blood that Ichiru has ingested to prevent his illness.

Shizuka Hio
Zero's Pureblood master when he was bitten by her when he was a child. She taunts and teases, when she comes to the Academy with Ichiru, about her being Zero's Master.

Yuki Cross
Yuki & Zero

Zero and Yuki have a very close relationship with one another. Having to live with her and Kaien when his parents were killed, Yuki has been the comforting and maternal caretaker of his. Soon, he grew to love her and even supported her relationship with Kaname. Zero feels extreme guilt when he bites Yuki, saying that he hates himself for doing it. After Yuki is finally revealed that she is a Pureblood and sister of Kaname, he broke ties with her and his hate to Purebloods is the visible emotion he shows to Yuki. It is unknown how he feels towards Yuki when he enters into the Vampire Hunter's Association.

Kaname Kuran
Kaname &amp; Zero

Both despising each other to their very core, Kaname and Zero have a very hate-hate relationship with one another. The only thing that is keeping each other from killing one another is Yuki. They understand each other to a certain extent.

Plot Overview

 * Main Article: Plot Summary for Zero Kiryu

Zero fights to keep his secret from Yuki until he bites her, overcome by his hunger. Following his horror and depressed state, he makes an attempt to run away and kill himself, but is stopped by Yuki. Though Yuki attempts to save him from falling to Level E by offering herself to Shizuka, Zero prevents it refusing to allow her to become a vampire. Zero attempts to kill Shizuka, but as she escapes when he discovers his twin brother still alive and serving Shizuka and causes Zero to lose his chance to drink her blood before she is killed.

Zero comes very near to falling to a Level E state when Kaname convinces Zero to drink his blood. Zero supports Yuuki in her attempts to uncover hidden past, but the discovery and awakening of Yuki as a pureblood partner causes Zero to sever their friendship. Zero is locked up by the Hunters Association when they decided they cannot control him when Ichiru comes to him and convinces Zero to "eat" him to complete the "Twin Piece" fragment. Though enemies, Zero assists Yuki in killing Rido and shortly after he declares that he will kill all pureblood vampires including Yuki. He fails to kill Yuki, instead he reveals his feelings for her and they part ways.

Zero now finds himself poised as the future president of the Hunters Association. In this capacity, he is forced to attend the peace meeting between the hunters and vampires and the vampire ball, while there he sees Yuki again for the first time in year. Zero continues to hunt vampires and seeks the truth about the Hunter's death at the party. Meanwhile he is still dealing with issues regarding his loss of his humanity. Despite his declaration of hostility against Yuki, when he meets up with an injured Yuki, Zero still finds himself assisting her.After that, Yuki jumps out the window as Zero clinches to his shoulder.