Shinobu Oshima secretly goes on a hot springs trip with her son, hiding it from her husband. Her son is deeply infatuated with her curvy figure, often clinging to her affectionately even in public. Shinobu, charmed by his innocent affection, gradually lets her guard down, drawing them closer. While relaxing in the woods, she's seduced by her son, slowly undressed, and overtaken by rising desire. Under the autumn sky, their forbidden passion unfolds. A journey of incestuous lust between mother and son, shared beneath the open blue sky.