[The popular doujin group "Clammbon" has teamed up for the first time to bring a live-action adaptation of their hit work, starring the healthy, busty beauty Nanami Nami!] When his step-sister suddenly confesses her love to him, his brother tries to reason with her and refuse, but he can't resist her overt and cute charms and he finally crosses the forbidden line. From then on, the two become unstoppable, spending their days entangled in each other's bodies, both at home and in a love hotel. Meanwhile, the brother is weighed down by guilt, wondering if their relationship is even permissible. Meanwhile, his sister, ignoring his doubts, becomes increasingly bold and advances on him... What is the "final decision" the cornered brother must make?