Arata Kaizaki is 27, unemployed, and hiding the fact that he quit his first job after only three months. A mysterious man named Ryou Yoake offers him a pill from the ReLIFE Laboratory that will make him look 17 again and re-enroll him in high school for one year as a social experiment. Arata accepts, but being a teenager again proves harder than expected. He fails tests, cannot keep up in gym class, and struggles to connect with classmates like the brilliant but emotionally guarded Chizuru Hishiro, who has troubles of her own.