Ai has been worried about her stepbrother Shinichi's bad behavior lately. He was a good boy when they first started living together as a university student, but before she knew it, he was not going to school and was messing around with the room. To top it off, Shinichi was making an ear-splitting noise every day, and Ai was fed up with him. Reaching her limit, Ai gave Shinichi a stern warning one day... But the next day, Shinichi, irritated by the scolding, made him suck his dick in revenge. From that day on, her life as her nasty stepbrother's mouthpiece began...