His lover's boyfriend came to the house to visit when he happened to meet his lover's sister in the bathroom, a personality girl named Yua Mikami, who was having sex with her boyfriend in her bedroom, and had a hobby of SM. After that, he peeked but he didn't expect Yua to find out a long time ago but still let him see. After that, he became passionate about this hobby and could no longer resist his lover's sister's lust.