Based on the erotic game by Black Lilith.

The evil stone conceives a part of the king of the hell's power in a different world. To prevent his revival, the stone is implanted into a body of a magical girl!
Now the clans from the hell follow after her.
The evil stone cannot be regained by a simple destruction of the body. Thus, they start disgracing the magical girl in various ways!

(Source: DLsite English)