That JAV

Your younger sister, Riku, is a bright, active, and honest schoolgirl. One day, when your parents are out of town, she brings a friend with her, and your tranquility is quickly shattered. While being forced to teach her homework, you are forced to do something dirty, and when you go to check the bathroom, you are taken in by a group of naked girls... Finally, due to over-aggression, you end up having sex with your own sister without wearing a condom.