Kyubei has been married to Ami for two years, but they still don't have any children. Ami's parents are eager to have a grandchild, so they come up with a plan. They ask Kyubei to abstain from sex for a month, and they will conceive a child with Ami during the family's hot spring vacation. Throughout the month, Kyubei struggles to control his sexual desires. Finally, the day of the family trip arrives. Upon arrival, Kyubei is eager to release all the pent-up desire from the past month. However, due to the long period of abstinence, Ami feels pain and refuses to have sex with him. In a moment of loss of control, Kyubei sees the perfect body of his mother-in-law. Unable to restrain himself, he engages in intercourse with his mother-in-law and impregnates her. Initially resistant, the combination of a massive penis and the youthfulness of the son-in-law makes Sayuri increasingly enamored with the sexual encounter. In the end, she surrenders herself, actively engaging with her son-in-law to enjoy the sexual pleasure, allowing him to impregnate her time and time again...