College freshman Gayeong Cha has never had a boyfriend, thanks to her overbearing older brother, Ganghyeon, who scares off every potential love interest. Desperate to win over her longtime crush, Gayeong buys a mysterious bracelet that promises to keep her brother out of her love life. She slips the bracelet onto the sleeping Ganghyeon's ankle and goes to bed happily, only to wake up in his body the next morning. Now forced to live each other's lives, the siblings’ college days quickly devolve into a disaster of misunderstandings, ruined reputations, and romantic chaos.