Every year on the ayu fishing season opening day, her husband returns to his hometown. This year, he decided to bring his wife along. At his parents' house, his father and younger brother live. The father is away on a two-day, three-night hot spring trip for a local association event. The younger brother is single and intensely desirous of intimacy with women. When he sees his sister-in-law entering the bath, that desire begins to stir…