Young Sister In Law 3 (2017)

Seok-yeong has been living with his father ever since his parents got divorced when he was young. His father, Joong-nam, who changes lovers frequently, would always introduce him to new girlfriends. As a result, it becomes very natural for Seok-yeong to run into strangers in their house and actually become more comfortable with older women than his peers. One day, his father says he’s going to marry his new girlfriend, Gyeo-won, and prepares a lunch out to introduce her. Seok-yeong eats together with his father, his prospective stepmother, and Gyeo-won’s younger sister, Gyeo-woon, to whom he feels attracted. However, Seok-yeong has to call Gyeo-woon his “aunt.” At the end, Joong-nam announces his plans to live with Gyeo-won starting that day.