After raising her son on her own since graduating from university, Kaede Sakuma is now excited to take a hot spring trip with him as he begins college life. As a mother, she feels genuine joy seeing her son grow, and she expects this journey to become a special memory. However, during the trip, her son confesses something important—he has begun seeing her not just as a mother, but as a woman. Driven by deep, instinctual desire, he makes a move on her. Though Kaede initially resists, she gradually succumbs to the overwhelming pleasure. Bound by a promise that this will happen only once, just for tonight, they enter into a forbidden relationship. Within the quiet serenity of the hot spring inn, the taboo emotions between mother and son grow stronger, leading them to passionate creampie-filled intimacy.