My Runaway Sister in law

Dong-gyu develops a special affection for his sister-in-law, Na-young, who takes such good care of him. His affection turns into obsession, and he eventually pretends Na-young has run away from home and sets up a new life with her. Initially obedient, Na-young eventually begs to be sent home. In an effort to secure her all, Dong-gyu introduces his ex-girlfriend to his brother.