Keita Suminoe, a third-year middle schooler preparing for high school entrance exams, lives with his twin step-sisters Ako and Riko, who compete openly for his romantic attention. Their parents not only tolerate the rivalry but actively encourage it, leaving Keita caught between his sense of propriety and his growing feelings. Each OVA episode drops him into another escalating situation at home, at school, or during study sessions that rarely stay on topic.