Shouta Handa, a 25-year-old without employment, despairs over his monotonous life. At a class reunion, he encounters his former female classmates and is stunned by their stunning appearances and successful careers. Unfortunately for him, they ridicule his lack of achievements and deem him a "loser" like before. One day, Shouta unintentionally falls into the school swimming pool while taking a smoking break, and a strange force thrusts him back in time ten years. Now, he is back in his younger body, surrounded by his classmates in swimwear during swimming class. Shouta must navigate his attraction to them and the undeniable closeness they share while grappling with his much older mindset.