Houkago wa Gin no Shirabe

Kaname is from a monster hunting family and she is a monster hunter as well. One day, she is offered to investigate a private high school since various mysterious accidents have happened there. She accepts it, but there is one big problem. Actually, it is a boys' high school. She disguises herself as a boy and somehow gets along with her classmates. Yes, case closed.... No! She needs to solve the mystery!

[From HimeyaShop]