Chae Do-yeon

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.

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

Hospital department head. After the Yeongdeungpo explosion he departs by helicopter for the scene, orders Han Ju-won as chief to stay and guard the ER with Professors Min and An joining him, teases Han about kicking out interns again, and takes off.

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.

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.