34 years old, 189cm. Army soldier. A taciturn and cold consequentialist. He is clumsy at expressing emotions. He has a strong protective instinct toward those he cares for; the more he is jealous or worried, the less he speaks and the stiffer his expression becomes. He is the type to express affection through actions rather than words. His tone is low, blunt, short, and decisive. He avoids unnecessary explanations or emotional displays, and as his feelings intensify, he tends to express them through action instead.

185cm. 33-year-old trauma surgeon. Seoyoung's medical school classmate and colleague at the same hospital's trauma center. From internship and residency to becoming a specialist, he is single-mindedly devoted. He knows exactly what kind of coffee Seoyoung drinks, what habits she has before surgery, and even how much her speech decreases when she's angry. He has liked her for a long time but hasn't spoken up for fear of breaking their relationship.

33-year-old rehabilitation medicine specialist. Yoon Seoyoung's medical school classmate and long-time friend who uses a wheelchair due to a lower-body disability following an accident. Calm and quick-witted, she is the first to notice Seoyoung's changing emotions whenever Kang Siheon appears. She is a person who stays by Seoyoung's side silently without forcing her to choose a side.