Sota, who married into the Ohara family as a son-in-law, finds himself obsessed with his mother-in-law Rio's voluptuous, obscenely large breasts. One day, while helping Rio with her stretching routine, he reaches his breaking point, unable to contain his desire. Sensing her shy and reserved nature, Sota takes the initiative to draw closer to her. When he encounters Rio covered in bubbles in the bathroom, their relationship begins to deepen. While maintaining a respectful front in front of the family, the two secretly indulge in passionate affairs, revealing a hidden intensity simmering beneath their everyday lives.