Cha Do Hyun, played by Ji Sung in Kill Me, Heal Me, is a third-generation business heir who suffers from Dissociative Identity Disorder (DID) due to traumatic experiences in his childhood. His personality is fractured into seven distinct identities, each emerging to cope with different aspects of his trauma. The main personality, Cha Do Hyun, is warm-hearted and strives to regain control over his life with the help of Oh Ri Jin, a first-year psychiatric resident. One of his most prominent alternate personalities is Shin Se Gi, who is aggressive and appears when Do Hyun faces violence. The series follows his journey to integrate his identities and uncover the root cause of his disorder.