Himitsu no Kankei -Nagisa to Sakura-

Sakura is a lively girl who is the center of her class's attention. However, she's also your faithful sex slave. This adventure game exposes the secret after school relationship between Sakura and her old buddy and current sex friend Nagisa, who happens to have an extra special body.

Exactly how their secret relationship ends is left up to you.

[From DLsite English]