Yuki & Zero

Yuki and Zero were childhood friends, allies who became enemies and finally into an uncertain wary relationship as they both try to figure out where they stand.

Background
Yuki and Zero met at ages 12 and 13 respectively, when Zero was taken in by Kaien Cross into his home. Yuki immediately took to the young boy and looked after him since the first night that she cleaned the emotionally fragile Zero's wounds. She promised to stay by his side forever after she discovered him distraught one night, tearing at his neck. Yuki would often stay up at night with Zero, patting his head after he had nightmares, helping him to fall back asleep. Yuki's nature overcame his distance and her presence also helped his nightmares to cease. Zero acted aggressively toward Yuki after learning of her love for the Pureblood vampire, Kaname Kuran, possibly also because of jealousy. When Zero freaked out fearing his turning into a vampire, he accidentally lashed out and hurt Yuki. When Zero was attracted to the smell of her blood to his shock, he swore to the Chairman, that he needed to become stronger. Yuki accidentally admitted she was scared by Zero. When Zero tried to tell her his secret, she revealed her fear about being attacked by the vampire in order to empathize with Zero. However it caused Zero's anger to flare up about himself and caused him to try and push her away instead of telling her the secret. This was the beginning of Zero deliberately trying to put distance between himself and Yuki, yet Zero grew attached to Yuki and his affection for her grew, to the point where he refused to be adopted by Kaien because he did not wish to become Yuki's family. When Yuki went to see Kaname at the school and was shaken by the encounter, Zero observantly told her if she was not scared, she should not shake. He is very protective of her, which Kaien used to his advantage after Zero stayed back a year of high school and continued to refuse to enter until Kaien told him that Yuki would then be a school guardian all by herself.

Zero's awakening
When Yuki discovers that Zero was bitten by a Pureblood vampire turning him into a vampire too, she began encouraging Zero to drink her blood so that he can survive knowing its against the rules. As the story progresses, he repeatedly demonstrates that his remaining life is for Yuki. When Shizuka offered Yuki a chance to save Zero from falling to a level E, she readily decides to give her own blood and humanity to Shizuka in exchange. However, Zero shows up in time to prevent the exchange from happening.

While dealing with his fall to level E, he has a nightmare about killing Yuki and almost kisses her after awakening and though he cites confusion as the cause, Yuki dwells on it for a short period until she concludes that Zero is precious to her,a fact that has still remained throughout the series since then. During a moment of weakness, she wonders if becoming a vampire will make her stronger and Zero vows he will never let her turn into a vampire. Realizing soon after that her question has hurt Zero, she finds it inexcuseable and decides that she must do away with the uncertainty that led to it. She desperately searches for the answers to her past and Zero tries to help her in her search, going as far as confronting Kaname on her behalf. He eventually ends up drinking Kaname's blood to his immense distaste in order to cease hurting Yuki with his hunger. Zero once told Yuki that he wants to die by her hand, and passed her a pistol.

A while later due to her trying to regain her lost memories, Yuki starts falling into her own madness and almost strangles Zero. When she asks him why he didn't try to stop her, he states that his life belongs to her. Upon hearing his response, she berates him and states that she has only been using him in the guise of helping him as a distraction from her own problems.

Yuki's re-awakening
When Zero discovers that Yuki is actually a Pureblood and Kaname's little sister, he becomes outraged and shocked. Though Yuki concludes she has no right to see Zero, she visits him in concern and in response to his declaration that all he senses behind the door is a controlling Pureblood who tampers with people's lives, she says that the Human Yuki that Zero knew is now gone, and that she has been eaten up by the Vampire Yuki. However, it is clearly seen that she regrets saying this, knowing that deep down she never wanted hurt him.

Zero and Yuki meet each other again upon confronting Rido, and although she desires to be allies once again with Zero, he declares her his enemy. The two however end up fighting together to defeat Rido, but after which Zero follows up by pointing his gun at Yuki and declares his intention to end everything by killing all Pureblood vampires including her. But he was unable to pull the trigger due to seeing Yuki's sincere and unwavering gaze that always gave him strength. He then relents that he didn't care if she had killed him instead. Following a confrontation with Kaname, Yuki was able to talk alone with Zero. He bites her one final time, then kisses her and finally embraces her while asking if her worries have been settled. Yuki confirms that they have and Zero tells her to go with Kaname. At their parting, he states that the next time they meet, he will kill her, to which Yuki agrees that she will run away from him in order to give him a reason to keep on living.

After leaving Zero, the shock of the evening's events finally catches up to Yuki as she realizes the implication of Zero's kiss. She laments that they will be enemies from now on and that she is not the one for Zero knowing that she can do nothing about being a vampire.

After a year
While confined to the Kuran mansion for a year, Yuki comes to terms with her vampire nature. She eventually realizes that her thirst can't be fully quenched because a vampire's thirst can only be satisfied with the blood of someone they love and a part of her heart is attached to Zero and it only gets worse.

Yuki and Zero had a clash at the vampire party, when Yori was searching for Yuki and was found by Sara. Yuki was slow to respond when she finds Zero manhandling Sara, she tries to intervene while laying her hand on Zero. Zero refuses to let go of Sara until Yuki stops touching him, to which she complies. When Aido invites Zero to join Yori in a private visit with Yuki, he declines.

When Yuki visits the graveyard and is attacked by Toma, Zero senses her presence and investigates only to find her being attacked, he threatens Toma and makes him leave. An injured Yuki feigns wellness, but a short time after collapses, thus Zero scoops Yuki up and takes her to a nearby hunter safe house to recover. Before he can set her down, Yuki awakens to his nostalgic scent and she almost bites him to her distress. She frantically departs with an apology. But later berates herself for not being able to answer him better.

Zero's prickly attitude towards Yuki is noted by Aido who in turn taunts Zero, telling him he should go after what he wants (Yuki). Aido later retracts the statement, but advises Zero that Yuki is doing her best.The sentiment is later echoed by Yori to Zero who also notes that Yuki hasn't changed. Zero asks Aido not to interfere as he believes that Yuki doesn't wish for it.

New leadership of Vampire society
After the death of Hanabusa Aido's father, they meet again as Yuki chases after a rogue vampire who was kidnapping human children. They meet while capturing the suspect and exchange a few words, where Yuki internally asks whether Zero is alright. Zero, upon learning from Kaien Cross that Yuki intends to do something on her own, seeks out Aido. He informs the latter that she is planning something and that if he intends to help, he ought to speak either to her or Kaien Cross.

Zero and Yuki are civil with each other. She later assumes that Zero is in complete opposition to her plan and she expresses concern that he may be failling to level E after seeing his hunger attack through another girl's memories. Yuki and the nightclass join Zero and the hunters in pursuing bad vampires, but Yuki disagrees with Zero killing a vampire. Zero berates Yuki for her soft stance on vampire punishment and taunts her to subdue him with her bracelet if she disapproves. Due to her keeping the bracelet, (whether as a sentimental value of her ten years as a human or simply due to her attachment to Zero), it is speculated that this may further show that she has feelings for Zero seeing as how she refuses to use the bracelet against him.

Their next encounter was when Zero returned Maria to the Night Class dorm. He met Yuki at the stairs and she later asks for things between them to go back to the way it was in the past. In response to this, Zero states that she was acting strange since she hasn't drunk any blood in a long time and drags her out to the woods. Zero states their interests are the same and bluntly demands she drinks his blood from his wrist and she denies it. Zero states that she needs to regain control and he threatens to destroy the school if she doesn't. Yuki cries for him to treasure himself more, but she relents with the belief that they cannot move forward without hurting one another. Yuki then goes to drink his blood, but changes her mind and goes to bite Zero's neck. Before she bites him, she states that she is only drinking his blood for mutual interest and she asks him not to think about anything and Zero says he no longer thinks of her. Zero's words echo in her mind and she bites him, she sees a vision of the fragments protecting Zero's fear in a coffin, one of them being the human verison of herself. Zero tells her to stop peeking inside his mind and she tells him that she wasn't like him who had done it to her previously.

The following day during a routine encounter with Zero, she tries her best to act normal. When the hunters call Zero, Yuki preemptively attempts to protect him assuming the worst and when Zero gruffly tells her its not her business and pushes her away, Yuki is reminded of his old behavior. She later confronts Zero about his desire to kill vampires and insists he is the kinder than anyone else, prompting him to point his gun at her again, but she tells him to pull the trigger if he can. Zero later delivers Kaname's message to Yuki.

In the Anime
During the last episode of Vampire Knight Guilty, the parting of 46th Night is very different, instead of biting Yuki, then hugging and kissing her, he asks her to drink his blood to prove that she really has become a vampire. Zero is not surprised, but instead vows that one day, he would kill all Purebloods, including Yuki.

Their Relationship
Zero's tsundere and agressive nature keeps him from befriending people, ensuring that Yuki is the only one close to him. Yuki's sunny, stubborn, and silly nature allows her to ignore Zero's aggression and rudeness overriding his desires with her own, inadvertently bullying him. Zero's affection for Yuki causes him to fiercely protect her and be easily directed by her. His nature is primarily shy and he does not communicate his feelings towards her, though he expresses frustration in the form of bullying her at times, causing Yuki to think he didn't like her. He refuses to allow Kaien to adopt him, because he doesn't want to be related to Yuki, though when she expresses curiosity, he ends up being very rude to her.

Not until 20th Night, when Zero asks Yuki why she does so much for him, does Yuki begin to actually think about their relationship and how she views Zero, though no conclusion is shown from this. Yuki was almost completely blind to Zero's affection for her until 25th Night after he almost kisses her, it is speculated that from this point that she begins to see more in Zero. She takes his friendship for granted and becomes very reliant on him, she remains somewhat ignorant of his feelings, causing her to confess her love for Kaname in front of him on more than one occasion.

Following Zero's kiss in 46th Night, Yuki is finally made aware of Zero's feelings for her. Yuki confirms in 47th Night that she finally understands his earlier overtures, but her status as a vampire means they cannot be together even as friends as it hurts Zero too much, she reveals that she will lock up her feelings for Zero in her heart.

Yuki finally admits she feels something in return for Zero in 51st Night, but it doesn't not affect how she feels about Kaname. She does however feel it is unfair on Kaname and should not be allowed to stay by Kaname's side. Yuki continues to be protective of Zero's feelings and notes in the party how Zero perceives others like Sara as his enemy and she later notes his pain on seeing the vampire hunter girl having been turned into a vampire.

Following Yuki's revelation of being a Pureblood vampire, Zero's feelings of anger have been more obvious than his love for her. After the year timeskip, his love and bloodlust for her is left ambiguous. Both characters avoid calling the other by the names they once so comfortably used. Despite Yuki's ambiguous feelings, their relationship has been reset somewhat from the comfortable friendship because of their status as enemies, Yuki's awkwardness is on display when during a coincidental meeting in 60th Night, Yuki greets Zero with a "Good evening" and mentally berates herself for being unable to respond better.

Zero returns to assisting Yuki subtlely after she rejoins them. He assists by nudging Aido towards Yuki. When Yuki states that Zero disagrees with her school plans, Zero declines to comment instead of agreeing, though he later insists that she is too soft and they are still poles apart on their stance on punishing vampires. When Yuki states she needs Zero, he fails to take it at face value and instead sees her as acting strange, so his response is that she must need blood. Contrary to all belief including Yuki's, he volunteers his own blood, showing that towards Yuki, he is indeed most different.

Yuki at first denies his offer for his sake, but finally relents and instead goes to bite his neck with her own fangs, echoing her earlier desire to take what she wants with her own fangs.