Rino's father-in-law lives with his son's family, warmly interacting with his daughter-in-law as someone she can casually rely on—helping with hospital visits, household chores, or just keeping her company. She is kind, beautiful, hardworking, and always smiles warmly. When he discovers that she secretly masturbates during her daily routine, he's overwhelmed with conflicting emotions. Despite her devotion to the marriage, he realizes she remains unfulfilled at night, and his heart begins to waver. Unable to resist any longer, he crosses the forbidden line.