Sakura Shiho, who divorced 10 years ago, has raised Kouta on her own. Kouta graduated from university and got a job, but his commute takes over an hour. Shiho suggested he live on his own, but Kouta refused to leave the house. Moreover, he never went out on his days off, and he never brought friends or a girlfriend home. Worried, Shiho decided to take Kouta out for a change and invited him on a hot spring trip.