When Keita Suminoe's father remarries, he not only gains a new mother but also two elder twin sisters, Ako and Riko. Ako, the homely and mature former student council president, contrasts with Riko, the athletic and aloof previous disciplinary president. Growing up together since kindergarten, the siblings share a deep bond that eventually evolves into a romantic and sensual entanglement. As Keita approaches his final year of middle school with a sports recommendation from a different high school, his sisters, disappointed, coax him to reconsider. Yielding to their fervent pleas, Keita now grapples with high school entrance exams while navigating his sisters' amorous advances. Despite their parents' approval, Ako and Riko aspire to become Keita's future wife, prompting him to maintain a strictly platonic dynamic. Amidst the allure of two captivating girls vying for his affection, can Keita resist their persistent temptations?