Souta, who married a daughter of the Ohara family as an adopted son-in-law, spends his days captivated by the plump breasts of his mother-in-law, Rio. - One day, Souta decides to help Rio stretch. - Sota, who has reached the limit of his patience with the huge breasts swaying obscenely in front of him, attacks Rio. - Souta sees through Rio's timid personality and pursues Rio even more. - Their activities escalate, such as playing with Rio's naked body covered in bubbles in the bathroom, and secretly having an affair while the family is together.