Zero Kiryu

Zero Kiryu (錐生 零, Kiryū Zero) is one of the main characters of Vampire Knight and the only Vampire Hunter/vampire who appears in the story. Zero is Yuki's childhood friend and the only other Cross Academy Guardian. Zero carries the "Bloody Rose," an anti-vampire gun.

Character concept
Having created Zero after Kaname's character sketches were completed, Maturi Hino opted to give Zero a casual feel in order to contrast him with Kaname's formal nature; the result was an ordinary guy who turned out to be a juvenile delinquent. Zero's personality was defined third. Hino and her editor were concerned Zero would be overshadowed by Kaname and made a concerted effort so that he would not appear to be a weakling. Matsuri Hino described Zero as exemplifying her hesitant nature.

Name

 * Zero was not the character's original name, which was changed in order to be stronger.
 * Zero's first name is the kanji for rei, meaning "zero."
 * In his last name, Kiryu, the ki means "auger" or "drill," and the ryu means "life."

Appearance
Zero is considered attractive by a few Day Class girls though depressed and scary by others. Shizuka Hiou stated after meeting him as an adult that he had become very handsome. Zero bears a tattoo, the Hunter's Seal, on the left side of his neck originally used to suppress 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 three silver earings on his left ear (top) and 2 on his right (bottom). His hair is a pale, silvery white, he had impressively pale skin well before being transformed, and his eyes are pale lavender or amethyst coloured in the anime and are portrayed as even lighter in the manga.

Personality
Zero is a composed character though occasionally he can be very cruel and hostile, particularly to Kaname. Zero is a gentle person though appears otherwise, he builds barriers around himself rather than opening up to Yuki. He has a kind heart and longs to protect humans and will never betray the one he holds dear.

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.

History
Zero was born to a prestigious vampire hunter's family. Zero, along with his identical twin brother, Ichiru, and Kaito Takamiya, was trained as a vampire hunter by Toga Yagari who frequently looked after the twins when Zero's parents were out hunting. Yagari lost an eye protecting Zero, when the still naive Zero made 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 danger of seemingly innocent vampires, Zero promises Yagari that he will never regret losing his eye to protect Zero.

Four year ago, Zero and Ichiru found Shizuka Hio sitting in a tree, whom Zero recognised as a vampire and told Ichiru to stay away from her. A few days later Shizuka attacked his family, she bit Zero and she killed his parents, Zero passed out believing she had killed his brother as well.

After that attack Zero was taken in by Kaien Cross. Yuki approached him carefully and cared for him although he was cold and hostile at times to her. Zero kept his affection for her to himself due to her loving Kaname Kuran. 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 constant companions, Zero acting as Yuki's protector.

Yuki Cross
Yuki Cross and Zero Kiryu became childhood friends when Zero was sent to live with Kaien Cross after the murder of his parents by Shizuka. He has romantic feelings for Yuki, and despite the fact that she was actually a Pureblood vampire, he continues to care for her.

Ichiru Kiryu
Ichiru is the younger twin brother of Zero.

Shizuka Hio
The pureblood Shizuka Hio became Zero's master after she bit him the night of the attack on his family. She claims she did it because she knew Zero would grow strong and challenge her. Shizuka meets Zero again 4 years later at Cross Academy while disguised in the body of Maria Kurenai, though Zero recognizes who she really is. During a confrontation with Shizuka, she taunts him about being his master. Despite Zero's hatred of her for killing his parents, taking his brother away, and stealing his humanity, he finds himself unable to go against her commands, just as Shizuka claimed. Watching Yuki being threatened by Shizuka, Zero finally breaks free of her hold and manages to wound her. Shizuka escapes, but Zero is prevented from chasing her by a distraught Yuki, who'd previously realized that Zero had secretly intended to sacrifice his life killing Shizuka. Before allowing him to leave, Yuki makes Zero promise to return after taking care of Shizuka. However, to Zero's shock, by the time he reaches Shizuka, she has already been dealt the final blow by Kaname, who had been secretly waiting in the wings. Despite Kaname's guilt, Zero is blamed for her death by an angry vampire council.

Kaname Kuran
Zero disliked Kaname on sight recognising him as a vampire and has been his rival ever since. They are only tolerant of each other for the sake of Yuki Cross and Kaname can be often seen jealous of Zero when Yuki expresses care for him.

Powers
Zero is a highly talented vampire hunter and possesses the standard abilities to sense vampires from a great distance, accelerated healing and in spite of being a vampire, also able to wield anti-vampire weapons. Since he became a vampire, Zero is able to distinguish purebloods from other vampires and has gained improved healing abilities. Kuran Kaname explains that after he eats Ichiru he would become the world's strongest hunter. He, then, explains that he has the blood of Yuki because she was a pureblood, Kaname and Shizuka was as well. After completing the fragment Zero is able to transform the Bloody Rose into its evolved state, where it literally becomes a part of his body, however the cost is using a high amount of his blood.

Quotes

 * "Even if I loathe vampires...Even if I don't want to hurt anyone...I can't stop myself from lusting for blood." - Source?
 * "They are just beasts who took human forms!" - Source?