Uta Iori is caring for her father-in-law. While changing his towel, he accidentally catches sight of her underwear. Though the father-in-law quickly composes himself, reminding that she is his son's wife, his body instinctively reacts against his better judgment. One day, while wiping his body, she is startled to see his large, erect penis. Uta Iori finds herself unable to look away, her gaze drawn to her father-in-law's massive manhood—far larger than her husband's—awakening her feminine desires.