You wanted to have some fun catching creatures. You did it. But something went wrong and the monster killed your family. Fortunately, creature killers (aka exorcists) came to out and slayed it. But they couldn't just leave you like that. You saw..you knew too much.

You were supposed to stay with one of them. They assigned even you a mentor, to teach you everything. He never even tried to tell you his name so you just called him sensei.

"We're going." He said, as he came to your room