BIOGRAPHY OF AO NO EXORCIST
This is the story of two parallel worlds: the human and demon world (Geneha), but none of the worlds can access the other. One day, the most powerful demon Satan possesses a woman fathering two children: Rin and Yukio Okumura. After that incident, they both are raised by a priest named Shiro Fujimoto, who is killed by Satan when he prevents Rin and Yukio of being kidnapped.
Rin was determined to avenge the death of whom he considered his only parent. He decides to join Vera Cruz Academy to become an exorcist with the help of the sword Kurikara which awakens the powers of Rin and starts new battles.