Love x Holic: Miwaku no Otome to Hakudaku Kankei The Animation

“In a world where humans and demi-humans coexist, Taichi Amano has by accident drank some blood of Kuon Aoe, the most popular girl in the school. Drinking her blood changed his body to have a special constitution which awakens demi-humans.
In exchange for protecting Taichi from whoever would target him, the Aoe house made him cooperate with awakening Kuon.”