When Kosuke's home water pipes burst, forcing him to stay elsewhere for several days, he ended up lodging at his friend Ichiro's house. Secretly a butt fetishist, Kosuke had long been captivated by Yuu, Ichiro's wife, especially her back and shapely curves. One day, he accidentally caught sight of her in sexy lingerie, provocatively thrusting her hips. Overcome with arousal, Kosuke, still fully erect, nervously asked her to apply beauty oil on him. Seeing his flustered state, Yuu gently smiled and allowed him to touch her. As their daily interactions continued, their relationship began to shift into something entirely new.