Zero Kiryu

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

Personality
Zero was a quiet and gentle boy, his twin, Ichiru questioned whether he was even capable of being a hunter. His gentleness even caused Yagari to lose an eye protecting him because he trusted an ex-human vampire. However after Shizuka's attack, Zero developed a deep hatred and distrust of vampires, he became withdrawn and sullen suffering from Avoidant Personality Disorder. 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 people (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 harbours 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 Yuuki. He tries to help Yuuki resolve her own problems and the impresses upon her that its okay for her to burden and use him because he owes her.

He is even more aggressive and rude towards vampires, however early on the shows hesitation toward destroying Level E vampires because they remind him of himself. Zero harbours a great deal of anger particularly toward purebloods because of their mechanisms in his life in particular, he extends this hostility toward Yuuki as well after she turns into a pureblood.

Zero is shown to have a soft spot for Yuuki and is also very protective of her, extremely afraid of hurting her.

Following the time skip Zero still fights severe hunger and controls it by hunting vampires at night, however his fear of falling to Level E is abated thanks to Shizuka's blood. He retains the opinion that a normal vampire is always in danger of spiraling out of control. His desire to protect humans exceeds his desire to kill purebloods as he allows Kaname his peace negotiations, but expresses his doubt over Kaname's true motives.

Appearance
http://images4.wikia.nocookie.net/vampireknight/images/c/c9/ZERO_KUN.jpg

His height is 184 cm (5' 11.3"). He has short silver hair with long bangs and light lavender eyes. He has very pale skin, even paler than the Night Class students. He bears a tattoo on the left side of his neck. He is usually shown in his black 'day' class uniform which he wears incorrectly with the vest and red tie exposed from under his black jacket.

Past
Zero was born in a vampire hunters family. He had a twin brother named Ichiru. They were both trained by a man named Yagari. One day Zero heard that his (school) teacher turned into a vampire. Yagari was going to kill her. Out of disbelief Zero tried to protect her, claiming that she was a nice person. His teacher tried attacking zero due to her being in a level E state. Yagari jumped in front of Zero to proctect, hence Yagari lost one of his eyes. In the end Yagari killed Zero's teacher

Ichiru and Zero were really close twins. Due to Ichiru's frail body, he couldnt keep up with training. Ichiru always got sick, but Zero always there to comfort him. 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. Zero told Ichiru that it was a vampire and told him to stay away from her. Ichiru felt ashamed that he couldnt even tell a vampire from a human. Later that day Ichiru over heard his parents talking about how Ichiru wouldnt be able to keep up with his training. He took this as they thought he was just a bother and that Zero was the favorite and always would be. Ichiru ran out of the house in tears. Ichiru ran into that same vampire that he saw earlier that day. He saw that she was crying and asked her why. She told Ichiru that his family killed her lover. She asked why he was crying.

Later that night that vampire approched their house. Zero noticed this before his parents and ran outside. That vampire took zero and bit him, hence turning him into a vampire. His parents came out in an attempt to save Zero but they got killed. Next we see Zero laying on the floor with his dead parents, tell Ichiru to run but Ichiru did not run away from the vampire we find out was Shizuka. After that attack Zero had been adopted by Kaien Cross the headmaster of Cross academy,

Story Recap

 * Main Article: Plot Summary for Zero Kiryu

Zero fights to keep his secret from Yuuki 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 Yuuki. Though Yuuki 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 Yuuki 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, barely alive following a futile attack on Rido Kuran, Ichiru convinces Zero to "eat" him to complete the "Twin Piece" fragment. Though enemies, Zero assist Yuuki in killing Rido and shortly after he declares that he will kill all pureblood vampires including Yuuki. He fails to kill Yuuki, instead he reveals his feelings for her and they part ways.

Currently Zero has been hunting vampires and now finds himself presented 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 later to patrol at the vampire ball. Zero investigates the death of a hunter and rebukes Yuuki for trying to get involved.