A week before his wedding, Nana, his fiancée's older sister, unexpectedly arrives despite supposedly being away on a family trip. She confesses that she has fallen for him and wants them to sleep together. When he protests, she insists they are not family yet and keeps seducing him. He finally gives in, and Nana's stunning figure and mature allure quickly overwhelm him. They change positions and settings as he creampies her three times, leaving him wondering whether he should switch sisters after all.