I got this Info from Wikipedia.com
Yuki Cross / Yuki KuranYuki Cross is the adopted daughter of the headmaster of Cross Academy, a 15- or 16-year-old first year student, born on October 13, who wields the Artemis rod, an anti-vampire weapon given to her by Kaien Cross. She begins as a human, a Guardian protecting the vampire students' secret from the human students. Yuki is close friends with Zero Kiryu, who she becomes determined to help once she discovers he had been turned into a vampire, following which their friendship rapidly evolves. She has been in love with Kaname Kuran, a pureblood vampire, since he saved her as a young child, but her affection is later divided to include Zero as well. She is generally a kind, caring, cheerful, and comedic character, but she is very naive and careless girl, often portrayed as not being very smart, being a poor student due to the fact that she is a Guardian at night and student in the daytime, giving her little time to study and sleep. She is often kept ignorant by other characters who know more about goings-on, which results in her character feeling guilty for being unaware of the suffering of other characters. Hino Matsuri has described Yuki as a healing and soothing character, who exemplifies her justice side.
Towards the climax of arc one, Yuki is revealed to be a pureblood vampire. Due to the threat of Rido having returned to Cross Academy, Kaname awakens her, resulting in all her forgotten memories of her past returning. This revelation alienates Zero, but the two fight together to defeat Rido. The formerly close friends part ways after Zero tells Yuki he intends to kill all pureblood vampires, including herself, while finally revealing his feelings for her. Yuki’s response is left unknown until she later admits to Kaname of holding romantic feelings for Zero as well. Yuki's character makes little progress during the one year time skip, spending the entire time inside the Kuran mansion with Kaname.
Zero KiryuZero Kiryu is unique being both a Vampire Hunter and a vampire. Yuki's close friend and the only other Cross Academy Guardian, he was trained to be a Vampire Hunter by Toga Yagari. Zero carries the anti-vampire gun called "Bloody Rose”. Zero lives with Kaien Cross and Yuki, after being bitten by a pureblood vampire who also murdered his family. Due to the attack, Zero developed a deep hatred and distrust of vampires, despite originally being a gentle character by nature. Matsuri Hino described Zero as exemplifying her justice side.
Zero is a 17 year old male. The first arc of the story is spent dealing with Zero trying to overcome his fall into the madness, helped by Yuki when she pledges to feed him her blood. Yuki continually oversteps boundaries in helping Zero and he ends up preventing her from trading her humanity to Shizuka Hio in exchange for preventing his fall to a Level E vampire. Zero swears never to allow Yuki to become a vampire and attempts to help her with her own issues. Zero clashes with Kaname Kuran, who only allows Zero to live because Zero protects Yuki and Zero is eventually forced to drink the blood of Kaname to delay becoming a level E vampire. Following the discovery of Yuki's true nature as a pureblood vampire, Zero and Yuki severe their friendship. Perceived as dangerous, Zero is arrested by the Hunters Association and it is revealed that Kaname had been grooming Zero in order for him to defeat Rido Kuran. Zero is shot by his dying twin brother, forcing him to "eat" Ichiru to complete the Twin Hunter fragment. With this final act and carrying the blood of three purebloods, Zero becomes one of the most powerful characters appearing in the series. Zero and Yuki work together and defeat Rido, but Zero reveals his intention to end everything, to kill all pureblood vampires including Yuki. Zero hesitates to kill her, revealing he has been in love with her for a long time. The two part, as Yuki promises to run from Zero forever to give him a reason to live.
Following the one year timeskip, Zero has progressed from his dangerous state of mind, more concerned with maintaining peace between vampires and hunters, enough to find himself poised as the future president of the Hunters Association. Zero continues to hunt vampires and seeks the truth about the Hunter's death at the party, but he is still dealing with issues regarding his loss of his humanity and intense vampire hunger. However, falling to level E is no longer a concern, as he is a level D, and his body no longer rejects blood tablets. When he meets up with an injured Yuki, Zero finds himself assisting her and even almost allowing her to bite him.
Kaname KuranKaname Kuran is introduced as the pureblood vampire who loves Yuki and saved her from an attack by another vampire when she was five years old. Kaname is actually one of the most powerful characters in the series, revealed to be one of the original vampires and founder of the Kuran family, who was raised as Juri and Haruka Kuran's son after being re-awakened by Rido Kuran. During the first arc, Kaname spends his time working to protect Yuki, which includes killing Shizuka Hio and fostering Zero Kiryu's powers. The end of the arc culminates in his destruction of the Vampire Council, which attacked the school, fearing the return of the Kuran family as the rulers of Vampire Society. Kaname's inexplicable attachment and gentleness to Yuki is finally explained when Kaname awakens her true nature as a pureblood vampire born to become his wife. Kaname is forced to do so with the return of his enemy and uncle, Rido. As Kaname is unable to kill his master, he approaches Zero to kill Rido and free him from Rido. The attachment to Rido persists beyond the vampire's death and his remnant is later seen talking to Kaname, taunting him about his conflicting nature.
Following the timeskip, Kaname takes Yuki to their childhood home and solidifies his rule over the vampires and forges and new peace between the purebloods and the hunters. When Yuki reveals her attachment to Zero thinking rejection, Kaname instead impresses upon her his love, preferring to be killed rather than losing her. Kaname is haunted by the idea that he will one day lose Yuki by her sacrificing herself and he flip flops between the desire to lock her up or allow her freedom.