Kaii Bokumetsu Minchi-chan

Kira is in love with her classmate Minchi, a beautiful and cheerful girl. But one day he sees her fighting a monster and discovers her secret: she possesses supernatural powers which she uses to exorcise evil spirits. However, that is not the only thing that she hides, since it also turns out that she's an aggressive and dominant person who now blackmails Kira to accompany her on her missions.