Kaname & Zero

From the beginning, the rivalry between Zero and Kaname is apparent. Shared between them is their love for Yuuki. Zero hates that she is friends with a Vampire, indeed he suspects she wants to be more than a friend, and Kaname feels that Zero is ultimately trash, even more so considering that he is becoming a Level E. One of the duties of the Pure Bloods is to control and exterminate Level E Vampires... It's obvious Kaname would very much like to do this to Zero. However, he lets it be known that he is allowing Zero to live to act as a go between and a protector for Yuuki.

After Kaname murders Shizuka, drinks her blood, and steals a vial of it to save for Zero, he lets Zero take the wrap for it. The High Council's punishment for the crime of killing a Pure Blood is death. However, Kaname acts out of grace when he stops the High Council from arresting Zero, even though that means facing the members on his own. He protects Zero at the expense of his own life and his own reputation...

The vial of blood that Kaname saves from Shizuka, the blood that could keep Zero from transforming, Ichiru drinks.

In chapter 27, Zero and Yuuki go the Hunter's Association in hopes that they can learn something about her past. However, while there, Zero finds something about himself out in the Library of Records

But, Kaname does something else that's surprising considering his feelings for Zero. He informs Zero that he can extend the time until he becomes a Level E if he drinks the blood of a Pure Blood... In chapter 30, Zero even takes Kaname up on his offer and drinks his blood. But now, in a way, that means Zero is even more indebted to Kaname.

At more recent chapters (33 or so), it is revealed that Kaname helped Zero for the sake of making a bodyguard out of him so that he could protect Yuuki. Kaname wanted Zero to kill Rido for him