Kim Seung-hwan

Elderly patient lying in a ward bed with monitor leads attached; Han Ju-won touching those leads triggers Woo Jin-han’s intrusion.

Black-haired doctor who finds Han Ju-won on a hospital rooftop after a patient death, confides he cannot imagine losing family, then later declares he wants to become like Han. He resolves to start over, dresses carefully for work, is teased for looking sharp, has his necktie yanked off by Han as an infection risk, and eagerly treats a 17-year-old with chest pain while craving recognition.

Hospital doctor and colleague. Appears in the past intern conflict scene and later calls Woo Jin-han after the disaster broadcast, relaying that the chief wants him down immediately because the subway accident has thrown the hospital into chaos.

Kim Seung-hwan’s guardian. Arrives with their daughter, tearfully asks about survival odds and her husband’s suffering, decides to stop resuscitation, then breaks down at the bedside.

Third-year emergency resident. Comforts crying interns, explains the chief’s perfectionism and strictness are teaching not hatred, offers to tip the chief if things are hard, and urges them to learn beside Han Ju-won.

White-coat colleague with an ID badge. In the cafeteria he goads Woo Jin-han about Han Ju-won’s return and the old murder until Do-yeon stops him; in the flashback intern day he frets over ER assignment and dreads Han Ju-won.