Miki, who divorced 10 years ago, has been raising Naoya on her own. Naoya successfully graduated from university and secured a job. However, Naoya has not left his parents' house even though it takes him more than an hour to commute to work. He has never gone out on his days off, and he has never brought friends or a lover over. Worried about him, Miki invites Naoya on a trip to a hot spring to get him out of the house for a change.