Yuki & Kaname

Yuki Cross and Kaname Kuran have a long history and have a complex, if somewhat at times, mysterious relationship.

Background
It is mentioned both in the anime and manga that Kaname and Yuki Kuran were engaged to be married since they were children. This is a common practice among purebloods to preserve their bloodlines.

History
Kaname once declared that Yuki was born to be his wife ever since she was born. Yuki loved and adored her brother and was very protective of him. Since birth, Yuki was hidden away from the outside, locked in a single room with no windows and Kaname sympathized with her situation.

During an attack by Rido that killed Haruka, Juri sacrificed herself to turn Yuki human, knowing that Kaname would not be happy about it. Kaname found the unconscious Yuki and took her to Kaien Cross' home for Yuki's safety. Kaname was sad knowing that the next time Yuki woke up, she would look at Kaname with the eyes of someone that doesn't remember him. Yuki awoke alone in the snow while Kaname was fighting the vampires who pursued them. She was discovered by a vicious vampire who tried to devour her but was saved by Kaname whom she no longer recognized.

Yuki was silent and distant upon her arrival at Kaien's home. Kaname was forced to leave after Yuki grows frightened of him seeing his fangs and remembering the vampire who tried to attack her. Kaname goes to live with the Ichijo's under the watchful eyes of the vampire council.

Kaname is frequently tricked by Kaien into visiting Yuki when he recieved urgent messages of danger to Yuki. Yuki grows increasingly fond of Kaname during this time, her first words being his name. Her cute antics make Kaname laugh (Not normal for Kaname) and he fondly watches over her. Kuran would ditch his guards and visit whenever prompted as well as on Yuki's anniversary of her being saved by Kaname, which as a child, she referred to as her birthday. The human Yuki grew trusting and fond of the vampire, with a strong belief in his gentleness based upon his gentle caring of her. She soon fell in love with Kaname and was constantly eager for each visit and his attention.

After the creation of the school, Yuki went to visit Kaname. However the vampire was away, as a result she fell asleep on the stairs of the night class's hall, almost bitten by him, Kaname finds the vulnerable Yuki and takes her to his room where unbeknownst to Yuki, almost giving into temptation. Instead, he ends up biting Ruka in front of her and Yuki runs off in shock. As of that point, some distance is created between them, Kaname hoped this would help her understand the cruel vampire nature.

Prior to Yuki's Awakening
She does not seem shocked when she learns Kaname is a Pureblood, she thinks it will not change her opinion of him. After all, she admires and idolizes him. Kaname loves Yuki more than anything in the world. He is always protecting Yuki and deems her as the most important person in the world to him. He has said many times that Yuki is "his dear girl".

Since he is feared by the other vampires because he is a Pureblood and because Yuki had all of her memories when she was five years old erased, he is often very lonely. Few people are close to him. Yuki cares about Kaname so much, her heart beats like crazy when he’s around her. She loves Kaname while he himself adores and cherishes her.

However once more, Kaname is a vampire and what is more important, a pureblood. He cannot allow himself to step closer to Yuki and risk to hurt her...or even curse her forever by drinking her blood. This one fact demonstrates just how important Yuki is to Kaname, but it does not hold. As danger settles in on the academy, Kaname feels that the way to keep the always-in-danger Yuki from being more of a vulnerability than needed is to reveal her true nature as a pureblood.

As a child, Yuki always referred to Kaname as her "Onii-sama" following her turning human, she at first called him "Kaname" and later "Kaname-sama" as taught by Kaien. Later at school, she referred to him as "Kaname-senpai". Yuki revealed in 25th Night that she had been determined not to refer to Kaname as "Kaname-sama" in an attempt to reduce the distance between herself and Kaname, but accidentally finds herself using it.

Yuki's awakening
Kaname is forced to bite Yuki to save her from the danger of Rido Kuran. Kaname "awakens" her vampire side. Yuki is initially disturbed upon her awakening at the thought of being in love with her brother, but then Kaname reminds her that they are engaged and she remembers their mother and father were also siblings and that Kaname promised someday they will be just like them.

When Kaname wants to leave the school with Yuki, she refuses on the basis that she needs to fight Rido ,don't want Kaname angry, sad so she kiss him and promises will return to his arms. After the fight is over and she parts with Zero, she returns with Kaname to their family home. There Kaname finally confesses all that he has done to protect her, including using Zero's bond with Yuki. Yuki is initally upset, but realises that she is hurting Kaname by pushing him away. She accepts responsibility for his actions that are done in her name.

Yuki stays inside the Kuran mansion for a year, to keep her protected and to learn how to use her fangs again. Yuki has returned to calling Kaname "Onii-sama" and occasionally "Kaname-senpai" despite his repeat requests to simply call him "Kaname". Kaname is frequently away and she looks forward to his returns. She suffers from bloodlust and hunger, desperate for Kaname's blood. She reveals that Kaname alone cannot satisfy her hunger and expects Kaname to reject her request to stay by his side.

Kaname accepts it and tries to impress upon Yuki his need for her, causing her to wonder "why it was [her]". He goes as far as telling her that she would have to kill him if she left him. He returns the Artemis to Yuki and Yuki remembers his words. She takes this as his approval to do as she pleases.

Yuki leaves the house and gets into trouble after being attacked by another childish pureblood, Touma, whom Kaname severly punishes for hurting Yuki. Kaname then reveals that he fears losing her deeply as has happened before to him.

Kaname the ancestor
After finally telling Yuki that he is not her real brother, Yuki drinks Kaname's blood to see his memories, she sees his awakening by Rido, which includes the murder of her true brother and Kaname's distant past as the ancestor who saw the rise of vampires. He fought to ensure humanity's survival, following another vampire who created the hunters and saw her death which created the Vampire Hunters and greatly affected Kaname.

Yuki asks Kaname if the hooded woman can be replaced, Kaname assures her that no one is ever a replacement for another, inadvertently refering to Yuki herself. Kaname eventually lies down to sleep forever after all his companions die and he is the last left of the ancestors.

Yuki awakens from the memories and frantically searches for Kaname after finding herself alone and confused. She finds Kaname and expresses her upset that she did see her brother's face upon waking. Kaname understands that its hard for Yuki not to think of him as her brother since he took her brother's life. Yuki understands and says she will call him "Kaname" from now on.

Aido-dono asks Yuki if she would be able to stop Kaname if she thought he was doing something she disagreed with and Yuki states that she will not be about to do anything while she is still not Kaname's equal. Her vampire inside expresses the desire to devour Kaname completely and tells her she will go crazy if she does not eat what she wants. Yuki acknowledges she has been too busy with her problems to consider other things.

When Yuki stumbles over calling Kaname by just his name, Kaname offers to let her rename him if she is jealous. Kaname asks Yuki what she thinks of him, she tells him that she knew him as her brother, her senpai and now he is the ancestor. She says that Kaname is a beast like her, but he is a bit weak, lies, is dodgy and has too many secrets. She is also a bit uncertain of his feelings for her, but amends that he loves her but there are other things mixed up in his feelings for her. Ultimately her best answer to his question is to ask if they can start over and she can watch him properly, to which he hugs her tight and agrees.