Coin

The hero of this game (default name Ryouta) is a typical hentai protagonist: a male teenager who is interested only in sex. One day, Ryouta finds a cute black bunny and brings it home; the next morning, the bunny turns into a sexy black-haired girl! Needless to say the activities the two perform during the course of the game do not include playing chess or discussing philosophy. But Ryouta is not satisfied with the "bunny girl" alone, what with all those cute female schoolmates around him...

[From Moby Games]