Yoo Chaewon has loved Kang Uihyun—her older brother’s best friend—for as long as she can remember. Despite knowing her feelings, Uihyun always keeps a firm distance, treating her as someone he must protect rather than love. Their long-standing relationship begins to crack when he suddenly brings another woman to his birthday party, forcing Chaewon to consider giving up on her 17-year unrequited love. But as she starts pulling away, Uihyun slowly realizes that the girl he thought he only needed to protect has become someone he cannot let go of.