Toshio Furuda, a salaryman promoted to branch manager, faces fierce family resistance when relocation to Hokkaido is required. His wife Kazuko and son Minoru refuse to leave their commitments behind, causing him deep distress. After a drunken farewell party, he falls from a pedestrian bridge, striking his head. The injury induces amnesia, psychologically regressing him to believe he is thirteen years old. This fractures his memory of his adult life and relationships.

Discovering photo booth stickers of himself with a high school girl named Emiri in his wallet, Toshio becomes fixated on her. His family suspects an affair, but the truth is mundane: Emiri merely assisted the intoxicated Toshio at a phone booth, leading to the accidental photos. She later returns his lost money and credit card, confirming their interaction involved no impropriety. Despite this, Toshio develops a persistent schoolboy infatuation with Emiri, intensifying his family's strain.

His condition lingers, frustrating Kazuko and Minoru. Following a heated argument, Toshio flees towards his deceased parents' home. Found crying at the train station by Emiri, he reveals he cannot recall his parents' location. His family apologizes and agrees to move to Hokkaido with him. This decision abruptly triggers his memory's return; he recalls their earlier request for crab and corn. The family relocates together. Toshio maintains a platonic correspondence with Emiri, sending her Hokkaido produce. Medical assessment attributes his amnesia to stress, not physical trauma.