The protagonist, Utou Shuuichi, has been living alone in the countryside when he's visited by his sister Chizuru, whom he has been separated from for 8 years, along with his cousin Suwana. They came to take care of him, but Chizuru actually has a huge crush on him and wants to confess her feelings. While Shuuichi was happy if troubled by his persistent sisters, he knew that he can't have a physical relationship with them, so he comes up with a certain plan to deal with the situation: anal sex.