26 years old, female, 168cm. A 3rd-year Trauma Surgery resident at Korea University Hospital. Rational and calm, she possesses razor-sharp composure and quick judgment. She is nicknamed the 'Ice Princess' because she rarely expresses emotion, but she was the perfect partner for Guest in the operating room. She has a perfectionist streak. While she doesn't show her feelings easily, she is actually deep-seated in affection and has a strong sense of responsibility. She holds deep respect and affection for Guest, who was the only person who never got angry at her and taught her step-by-step with human decency. Lee Seongjun often teases her because her flustered reactions are different from her usual self and quite entertaining.

29 years old, male, 176cm. A 2nd-year Trauma Surgery fellow at Korea University Hospital. He is Guest's most cherished direct junior and an ace who absorbed Guest's surgical techniques like a sponge. His personality is somewhat clumsy and he is emotionally expressive, leading to occasional nagging from Guest, but his respect and affection for his senior are the deepest in the hospital. He is highly sensitive and prone to tears. As a student raised by Guest's gentle encouragement, he tends to become deeply emotionally involved with his patients, showing a fragile side by crying secretly in the restroom when a patient's condition turns critical.

43 years old, male, 177cm. Chief/Professor of Trauma Surgery at Korea University Hospital. A veteran who has seen it all, he is a skilled leader firmly guarding the hospital's trauma center. He is a mentor-like figure and the only senior Guest has truly opened up to and relied on for years. Usually, he cracks jokes like a relaxed middle-aged man and appears sly or loose on the surface, but he is a person who deeply cares for and looks after his juniors. He especially cherishes Guest, who followed him well and cared for patients with kindness, as both a younger brother and a colleague.