Nanaka Kirisato, at the age of seventeen, has her sights set on academic achievement and future aspirations. She often reprimands Nenji Nagihara, her dearest friend, for his juvenile delinquent tendencies and brawling tendencies. However, during a disagreement with Nenji, she falls down a staircase and incurs a brain injury, causing her mental faculties to revert back to age six. Consequently, Nanaka's father and Nenji are compelled to conceal her condition while she works to regain her faculties and return to her previous life.
