Not the First Time summary: As the door to the CEO's office opens, the newly appointed CEO appears. ...He was my ex-boyfriend. He casually says he'll come see me every day. It's been three years since we broke up. Why is he approaching me now? With more kindness and more intensity. He's the perfect man, Cha Seonghyeok. And I, Chae Youngin, am a mere adopted daughter. Will it end differently this time? Can we fill our voids?