Ten years after divorcing her husband, KAORI continued living with her son Kota in a small house on the outskirts. Since Kota had a one-hour commute to work, KAORI suggested he move out and live alone, but he hesitated to leave home. Seeing that he stayed indoors even on weekends instead of going out with friends, KAORI grew concerned and wanted to cheer him up by getting him out of the house. With that in mind, she decided to invite him on a hot spring trip.