Ao no Exorcist 青の祓魔師

Blue Exorcist (青の祓魔師（エクソシスト）, Ao no Ekusoshisuto^?, is a manga wrote by Kazue Kato.

The story revolves arround Rin Okumura, a teenager posessing abnormal strength and endurance who was raised by Father Shiro Fujimoto along his younger twin brother Yukio. Soon after Yukio departs to study at the prestigious True Cross Academy, Rin learns that both he and his brother are sons of Satan, the strongest of all demons. 

Witnessing Shiro dying to protect him, Rin ends up doing what his guardian asked him to never do, draw the demon-slaying blade Kurikara that restrains his demonic powers, from its scabbard. From that moment on, Rin not only gains permanent demonic features like fangs, pointed ears and a tail, but also the power to ignite himself into blue flames that can destroy anything it touches.

On Shiro's funeral, Rin has an encounter with Mephisto Pheles, who agrees to his wish to become an Exorcist like his guardian to take revenge on Satan. He enrolls at the True Cross Academy, which is actually the Japanese branch of an international organization dedicated to protect the human realm, Assiah, from demons and other creatures from the demon realm, Gehenna. Rin takes part on the special Exorcist course only known by a few and much to his surprise, he finds that his brother Yukio is already a veteran Exorcist and will be one of his teachers.