Yuki is a high school student who has a close relationship with her older brother. In fact, many would call their relationship somewhat intimate for siblings. The truth of the matter is, these two blood relatives have been having sexual intercourse for multiple years. However, when Yuki's brother starts attending university, he finds himself a normal girlfriend and tries to end the taboo relationship with his sister. But Yuki is unwilling to comply, and she continues to make daring advances on her beloved brother. [Written by MAL Rewrite]