Haruka & Kaname

Haruka Kuran was Kaname Kuran's father.

Background
Kaname Kuran became Haruka Kuran's son after Haruka's actual son (also named Kaname) was killed by Rido Kuran in order to awaken Kaname the Ancestor. Despite this, Haruka and Juri Kuran raised him as their own and later Juri gave birth to Yuki Kuran, his sister and fianceé.

Plot summary
Haruka and Juri Kuran's first child and son Kaname, was kidnapped by Rido and killed in order to awaken Kaname the ancestor. However, this Kaname took the form of a baby and therefore replaced Haruka's real child, but resembled Haruka greatly. Despite knowing this, Haruka and Juri still raised him as their own son without any spite or hatred.

However, after Rido discovered Yuki's existence, he came back to the Kuran Mansion and attacked it so that he could also kill Yuki. Haruka fights Rido to protect Yuki and easily takes down two servants and controls two others, turning them into a beast before ordering it to attack Rido. Kaname enters the scene and notices that Haruka is wounded by a hunter's sword and runs to his aid. Kaname then uses himself as a barricade between Haruka and Rido, to which Haruka objects and embraces Kaname stating that it will shatter his pride as a parent if he let Kaname protect him. Kaname then tries to tell Haruka that he isn't really his son and corrects himself after he calls Haruka "Father" calling him "Haruka" instead. Haruka responds saying that he knows everything and that Kaname has been his adorable son and always will be. Haruka then shatters into many pieces as he dies around Kaname. Kaname then proceeds to try and kill Rido by using the same sword that had killed Haruka, but Rido reminds him that he could never kill him as he is his master. Kaname unfazed by this obliterates Rido's body as this is the closest he can get to killing Rido.

Their relationship
Haruka has always considered Kaname as his son regardless of the fact he isn't and is the reason behind his true son's death. However, Kaname seems to be unable to fully bring himself to consider Haruka as his father because of this fact and so, continues to feel guilty about the occurrence.

Nonetheless, the two are very close to the point they are both more than willing to die in order to protect the other as shown in the 38th Night. Also in this night, it is suggested that Kaname did not know that Haruka and Juri knew who he really was (when he tries to explain his true-self) as they both treated him as their son. This may have been what caused Kaname to never fully bond with Haruka or Juri as he may have thought that the truth would cause them to hate him.

However, after Haruka's death, that final wall between the two would have been broken down as it is made clear that Haruka had unconditionally loved Kaname and so, allowed Kaname to make Rido's death even more personal besides the fact that he was a threat to Yuki.