Ten years after her divorce, Miki has raised her son Naoya all by herself. Naoya successfully graduated from college and secured a job. However, despite having a commute of over an hour, he continues to live at home, rarely going out even on weekends, and never spending time with friends or a girlfriend. Worried about him, Miki decides to invite Naoya on a hot spring trip in an attempt to reach out and connect with her son.