Rin Okumura is a teenager with a natural gift to get himself in trouble. Despite that he tries his best to meet the expectations of his twin brother Yukio and Priest Shiro Fujimoto, who acts as their guardian, until he finally learns about the dark secret behind his origin.

Fujimoto and his companions try their best to protect Rin from the demons who are after him, but he ends up posessed by Satan, the most powerful of the demons and Rin's father. Seeing his guardian taking his own life to protect him fron Satan, Rin decides to fight back by unlocking his demonic powers, even knowing that by doing it he would not be a human anymore.