Rio is under constant pressure to give the family a grandchild. At her father-in-law's suggestion, the whole family plans a hot-spring trip, but her mother-in-law orders a month of abstinence beforehand to improve their chances of conceiving. On the day of the trip, Rio's husband refuses her, while her father-in-law is likewise rejected by his wife. Both frustrated and horny, Rio and her father-in-law head to the baths to cool off—where he happens to see her bathing...