Mitsuki (Hinako Sakurai) is a cute and cheerful second-year high school girl. One day, her father Ren (Michitaka Tsutsui) and mother Rumi (Rei Dan) told her a shocking news that they both cheated on the same couple. After discussion, they decided to form a new family of six with the couple and their children. What Mitsuki didn't expect was that Ayou (Ryo Yoshizawa), who was about to become her brother, was studying in the same school as her. Ayou is a boy with handsome looks and powerful abilities, but for Mitsuki, Ayou's personality is a bit bad and he always likes to play tricks on himself. After starting a "living together" with Ayou, her good friend Gintae (Daiki Sato) suddenly changed his temperament and kissed Mitsuki forcibly, which made Mitsuki fall into confusion.