Kitsune no Akuma to Kuroi Grimoire

Kitsune no Akuma to Kuroi Grimoire (狐の悪魔と黒い魔導書〈グリモア〉) is a manga series by Yuu Tachibana. It was serialized in Shonen Ace.

Plot
Narrates the story of Kyuuki, a strong, proud fox demon who recently woke up and needs a host and Kamishiro Shin, a normal would be high school student if it wouldn't for "his ability" and for the fact that he got a hold of the black Grimoire that controls Kyuuki's existence.

Shin is bound to the book as long as he is alive, thus not only he can't sever his connection to Kyuuki; but those who want the book's power are bound to come after his hide regardless of time and place.