Erina is teasing her unpopular brother as a joke. The virgin brother takes the joke seriously and thinks she is trying to seduce him, so as soon as their parents leave, he inserts his penis into his sister. Erina climaxes from the force of it all, but her brother, who is not used to women, ignores her and continues to thrust his hips recklessly. Even after she climaxes, her brother continues to thrust his penis into her, bringing her to orgasm over and over again until her parents return home.