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. As a child, Yuki adored her older brother and the two shared a close relationship. Due to fears over her safety, Yuuki's birth was kept secret from the rest of vampire society, and for the first five years of her life, she was kept hidden from the outside world, locked in the basement of the Kuran manor with only her parents and older brother as companions.

Yuki's parents managed to keep their daughter safe until the night Rido Kuran attacked the Kuran household, killing Haruka in the process, and spurring Juri into sacrificing her own life in a final attempt to protect Yuki by transforming her into a human. After severly injuring Rido (but unable to land the killing blow), Kaname took the unconscious Yuki to the home of Kaien Cross, a vampire hunter and longtime friend of the Kurans. Upon awakening, Yuki no longer remembered the first five years of her life, instead beleving that she had been saved from an angry vampire in a snowy field by Kaname, giving Kaname the lasting impression of a savior in Yuki's thoughts.

Yuki then spends the next 10 years of her life living as Kaien's adopted daughter while Kaname is taken in by the Ichijo family under the watchful eyes of the vampire council.

During this 10 year separation, Kaname is frequently tricked by Kaien into visiting Yuki, opportunities which allow the two to grow close once again, and which gives Kaname a temporary respite from the vampire council. With Yuki, Kaname is able to laugh and relax and behave more like a normal teenager as he fondly watches over her. Kaname also makes it a point to visit Yuki each year on the anniversary of her being saved from the angry vampire, a day Yuki calls her birthday. The human Yuki grows trusting and fond of Kaname and holds a strong belief in his kindness based upon his gentle caring of her. She soon falls in love with Kaname and begins looking forward to each of his visits.

Yuki and Kaname's relationship changes after the creation of Cross Academy. Knowing Kaname is living nearby in the school's dormitories, Yuki decides to pay him a visit. Unable to locate him, she falls asleep on the dormitory stairs while waiting for him. Kaname finds her soon afterward nearly gives into the temptation of drinking her blood, stopped only at the last minute by Ruka. Kaname then takes Yuki to his bedroom and proceeds to drink Ruka's blood in an attempt to quell his hunger. Yuki awakens while Kaname is still drinking Ruka's blood, the scene causing her to run off in shock and fear. Finally having come to understand that vampires and humans truly are different from one another, Yuki's relationship with Kaname becomes more distant than it once had been, to the sadness of both.

Prior to Yuki's Awakening
At the beginning of the series, Yuki is 15 years-old and a first-year student in the Day Class at Cross Academy, where she also acts as a school Prefect/Guardian. As the Night Class president, Kaname is one of the most popular and influential students at Cross Academy, and seemingly unreachable for a normal girl like Yuki. However, the Night Class share a secret which only the school Prefects, Yuki and Zero Kiryu know: they are all vampires, and Yuki and Kaname also share a secret past of their own: Kaname once saved Yuki from a vampire when she was 5 years-old. Thanks to this, Yuki regards Kaname as her savior and the two enjoy a special bond. Kaname calls Yuki his "dear girl" and Yuki quietly returns his affections, though often feels awkward and inferior around Kaname due to his status as a respected Pureblood vampire.

Although Yuki states that she is in love with Kaname, she finds his attachment and his gentleness toward her inexplicable as Kaname spends much of the first arc working to protect Yuki, which includes killing Shizuka Hio and fostering Zero's powers.

Yuki's awakening
As Rido Kuran closes in on Yuki at the end of the second arc, Kaname bites her, reawakening Yuki's vampire side and returning the lost memories of the first five years of her life. Yuki is initially disturbed upon her awakening at the thought of being in love with her brother, but Kaname reminds her that they are engaged and that intermarrying is a common practice among purebloods as their mother and father were also siblings.

Kaname then suggests he and Yuki leave the school in order to escape from Rido, a plan Yuki refuses out of a sense of duty as a school prefect, and on the basis that she needs to fight Rido and wouldn't be able to forgive herself if she ran away. Kaname is upset at her refusal; however, Yuki kisses him and promises to return to him afterward. Yuuki keeps to her word, and after the fight with Rido ends, she parts with Zero and 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 accepts his sins and wishes to share the responsibility for his actions.

During the fight with Rido, Kaname destroys the corrupt vampire concil, an act which sends vampire society into disarray and earns him a number of enemies. Kaname spends the year following Rido's attack reorganizing vampire society and maintaining the peace. Afraid for Yuki's safety, Kaname has her remain inside the Kuran mansion during this time and limits her contact with the outside world requesting that Yuki neither write Yori letters, nor invite friends to come visit her at the manor.

Also during this time, Yuki returns to calling Kaname "Onii-sama" and occasionally "Kaname-senpai" despite his repeated requests to simply call him "Kaname." In addition, she experiences some difficulties relearning how to use her fangs and seems to be in a perpetual state of bloodlust and hunger, desperate for Kaname's blood. Although Kaname regularly gives her his blood, Yuki reveals that Kaname alone cannot satisfy her hunger; however, she asks to remain by his side despite this. Kaname accepts her request and returns Artemis to her stating that he would rather kill her or be killed by her rather than being apart.

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

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. Kaname eventually lies down to sleep forever after all his companions die and he is left the last of the ancestors.

After awakening from the memories, Yuki finds Kaname and the two discuss what she has seen. 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. Yuki declaires that she will call Kaname by his name from now on, rather than "Onii-sama" as she had been. She also states 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.

After saying goodbye to Yuki, Kaname leaves saying that he has very important duties to attend to, leaving Yuki alone in the mansion. Prior to his departure, 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. Yuki, still confused by Kaname's last remark to her and beginning to feel a sense of unease, runs out of the mansion hoping to find Kaname. Instead, she runs into Kaien and Aidou, and together, the three find Kaname with Aidou's father. To Yuki's shock, Kaname slays Aidou's father in front of them.

Soon afterwards, Kaname is marked as a "dangerous" vampire, and Yuki gets taken to the vampire hunter's headquarters for further questions. Unable to answer any of Kien's questions as Yuki doesn't know what Kaname's intentions are, the meeting ends. Yuki vows to keep the peace between vampires and humans, and also promises to find Kaname to ask him of his intentions herself.