Демоны-убийцы

Mikoto Rikudo, an ordinary high school student, lives a normal life and gives little thought to the unexplained appearance of entities called "demons." Everything is turned upside down when he learns that the most shy girl in his class is one of them, and he finds himself drawn into a battle with these creatures, becoming one himself... only to discover that he must either kill other people using his new powers, or die himself.