When Keita Suminoe's father remarried, he gained not only a new mother but also elder twin sisters, Ako and Riko. Ako is homely and mature, while Riko is athletic and aloof, but both share a close bond with Keita developed since kindergarten. However, their relationship has developed into something more romantic and erotic in their last year of middle school. Keita has received a sports recommendation for a different high school, disappointing his sisters who desperately plead with him to change his mind. Unknowingly, Keita now has to attempt to study for his high school exams while warding off the advances of his lust-driven sisters. With their parents' blessings, Ako and Riko strive to become Keita's future wife, but he tries his best to keep their relationship strictly platonic. Nevertheless, with two gorgeous girls vying for his attention, will Keita be able to resist their endless temptations?