Seongjeok Gwangye Baljeon

Seong Ji-Hyun reunites with Baek Ian, her high school crush. Ian's competitive nature, obsessed with defeating Ji-Hyun, had strained their relationship, and she thought they'd never see each other again after graduation. But when they finally meet again, Ian approaches Ji-Hyun in a different way, becoming obsessed.

(Source: Naver Series, translated)