Choi Hyeong-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.

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.

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

Former ER chief now at the hospital. A flashback shows him nearly driving out all interns. After the Yeongdeungpo Line 1 train explosion news, he calls the situation the worst, is ordered to guard the ER while the department head leaves for the scene, activates Code Gray, and as disaster response commander briefs staff on mass casualties and crowd control.

Kim Seung-hwan’s elder daughter, a student about to enter high school. Arrives at the ER with her mother in tears and sobs at the bedside after the death pronouncement.

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.