Kim Seong-hee

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.

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.

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.

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.

55-year-old man transferred after office chest pain, anterior MI on ECG, and no response to NTG at hospital A. He still has pain and dyspnea, asks staff not to tell his family because of his high-school daughter and tired wife, but Han refuses. He later goes into V-fib requiring CPR.