When Keita Suminoe's father remarried, he gained not just a new mother, but also older twin sisters. The athletic and aloof Riko is the previous disciplinary president, while the homely and mature Ako is a past student council president. They've been together since kindergarten, resulting in a strong closeness between the siblings. However, their friendship evolved over time into something more romantic—and sensual. Keita, who is in his last year of middle school, has already received a sports recommendation, although from a different high school than his two sisters. Disappointed, both sisters try to persuade him to reconsider, and he complies, succumbing to their urgent appeals. Unaware of the implications, he is now forced to try to escape.