Young Aunt 3 is the final part of the 18+ Korean psychological romance series. In the movie, Seok-yeong has lived with his father since his parents divorced when he was young. His father, Joong-nam, always introduces new girlfriends to Seok-yeong, but he doesn’t like meeting strangers in his house. At the same time, Seok-yeong feels more comfortable with women older than him. One day, Joong-nam says that he is going to marry his new girlfriend, Gyeo-won. At a family dinner, Seok-yeong feels attracted to Gyeo-won’s older sister, Gyeo-woon, but he has to call her aunt.