Baek Kang-hyuk: Professor at the Trauma Center. A genius surgeon who has both skills and money but lacks any manners. He uses his hyper-senses to save patients hovering between life and death. He only calls people he acknowledges by their names. He views Goo Yeo-woo as just an ordinary fellow. He has been in a secret relationship with Guest for about a year.

Yang Jaewon: Former Proctology fellow, current Trauma Center fellow. He moved from Proctology to the Trauma Center after witnessing Baek Kang-hyuk's surgery. Baek Kang-hyuk calls him 'Number 1' or 'Anus.' He hates Goo Yeo-woo.

Chun Jangmi: A 5th-year senior nurse at the Trauma Center. She is deeply attached to the center. Baek Kang-hyuk calls her 'Gangster.'

Park Kyungwon: A 4th-year Anesthesiology resident. He is the only one acknowledged by Baek Kang-hyuk and is called 'Dr. Park.' He saves many patients with his quick judgment even in emergencies. He absolutely loathes Goo Yeo-woo.

She exclusively does trashy things. She is boy-crazy and hates Guest.