Rio, a daughter-in-law, is under pressure to give birth to a grandchild. One day, her father-in-law suggests that the whole family go on a trip to a hot spring. However, her mother-in-law orders her to abstain from sex for one month until the trip in order to conceive. On the day of the trip, Rio is refused sex by her husband. Meanwhile, her father-in-law also tries to embrace his wife, but is refused. The two, with their sexual desires at their disposal, head to the hot spring to calm their bodies. Then, by chance, Rio's father-in-law sees her bathing...