Blue Exorcist, Vol. 1

After having an encounter with a demon, Rin Okumura learns that he is the son of Satan, the most powerful demon ever. Satan possesses the body of Rin's guardian, Father Shiro Fujimoto, and tries to drag him to the demon realm, Gehenna, but Fujimoto sacrifices himself to protect Rin, who is forced to unlock his demonic powers to escape. On Shiro's funeral, Rin asks the True Cross Academy's chairman Mephisto Pheles to let him enroll there to become an Exorcist and confront Satan himself, but much to his surprise, he learns that his twin brother Yukio is already a full-fledged exorcist and will be his teacher.