The story begins with Keita Suminoe, a male third-year junior high school student studying for his high school entrance exams. He lives with his older twin stepsisters, Ako and Riko, who are not related to him by blood, and they help him prepare for his exams. Although he initially feels conflicted about it, he starts to develop feelings for his two stepsisters, and his parents encourage him to eventually marry one of them.
