Hoozuki -Kakusei-

You open your eyes after a hellish and terrifying nightmare, only to discover a crack in the dimension. From that crack appears Ku'on, the little boy who used to play with you when you were a child. Saying that he needs your help, Ku'on drags you into the crack. The two of you get separated and soon you learn that you’ve arrived in a world where Oni exist. Who will you encounter in that world…!