The twins, Momoka and Koume, and their older brother, Ouji, are step-siblings with no blood relation who became a family through their parents' remarriage. The older sister, Momoka, has a plain appearance and a reserved personality, while the younger sister, Koume, is a bright type who loves putting on makeup, dressing up, and looking cute. Despite being twins, they lived completely opposite lives, but in reality, both of them harbored romantic feelings for their older brother. Their feelings for him were an absolute secret that they couldn't even tell each other as sisters. However, one day, Momoka witnesses Koume kissing their sleeping brother. From that point on, the story depicts how the relationship between the three close siblings begins to change