HYEONGUI SEONBAE

After returning from studying abroad, In-Jun is heartbroken to hear that his (ex-)lover Se-In has been marked by Jae-Gyeong, who is rumored to be a promiscuous bastard. While walking away from In-Jun towards Jae-Gyeong, Se-In doesn't see the huge truck hurtling towards him. In-Jun and Jae-Gyeong throw themselves into danger to save him, and are caught up in the accident. When In-Jun finally wakes up, he's shocked when he looks in the mirror... He's now in Jae-Gyeong's body!!

(Source: MrBlue, translated)