Headmaster Kaien runs Cross Academy with the idea that vampires and humans can live together.
Headmaster Kaien Cross is the founder and Headmaster of Cross Academy. He is also the adoptive father of Yuuki, the heroine. Kaien found her while she was wandering with Kaname Kuran after he saved her from a hungry vampire. He took her in and be came a slightly odd father, this often annoys Yuuki. Kaien is the guardian of Zero Kiryuu as well, whose family was killed by vampires. As the headmaster of the school, he appointed his children as guardians, to protect the school and get both classes form getting too close to each other. (Night class being vampires.) Headmaster Cross seems to have all ties to the vampire and vampire hunter communities. Kaien was also formerly a vampire hunter as well though his stance is now neutral. It has been reviled that he has been indebted to the Kuran family as well.
His personality is a bit of a mystery. Most of the time, he seems idiotic. However, under this cloud of stupidity he seems to be somewhat ruthless. He appears to have his own agenda. Kaien somewhat promotes Zero, Kaname, and Yuuki in ways that lead them to develop their own relationship, it suits his wishes.