しすたぁ孕すめんと♪

There's one night the protagonist found out his little sister was masturbating while thinking about him. That made him lost himself to rape her. And it began the forbidden love, but his classmate Satsuki found out their relation as soon. Satsuki was trying to prevent him to going to the wrong way, and Ayami was afraid he was being taken away by Satsuki. There began the sister and classmate fighting over the protagonist.