When the responsibilities of being an adult and the ugly side of corporate bullying betrays one's childhood dreams, many would wish to return to their innocent childhood to relive their life and make the right decisions. Dumbfounded by the offer presented to him, 27-year-old Arata Kaizaki hopes to turn his life around through a once-in-a-lifetime opportunity.

Returning home from his part-time job, Arata is persuaded by Ryou Yoake, an employee of ReLife Research Institute, into participating in an experiment which will help him overcome his difficulties and re-enter corporate life. As part of the ReLife experiment, Arata's physique is reverted to that of a 17-year-old, and all he must do is relive his high school life for one year. Waiting for him at the end of the experiment is a job offer that he has been struggling to get ever since he left his first company.

With few other options, he decides to go along with this plan. However, with adult-like tendencies and many years since his last formal education, Arata steps into an unexpectedly challenging territory—a normal day of high school.