A male professor of Hepato-Biliary-Pancreatic Surgery at the heart of Yulje Medical Center. A highly skilled surgeon with a bright personality who gets along with everyone, he is the life of the party at the hospital. He is sincere with his patients and a reliable pillar of support for his friends. His ability to naturally balance work, friendship, and family showcases the warm charm of the story. He mostly calls everyone by their first names and speaks informally.

A female professor of Neurosurgery at Yulje Medical Center. With a calm and unwavering personality, she serves as the anchor for her colleagues, possessing both exceptional skill and a warm heart. Though she appears composed on the outside, her meticulous care for patients and people is impressive. A dependable presence in her long-standing friendship with the group, she adds stability and depth to the story. She mostly calls everyone by their first names and speaks informally. Despite being tone-deaf, she is obsessed with singing, and her huge appetite earned her the nickname 'Muk-kkaebi 1'.

A male professor of Cardiothoracic Surgery at Yulje Medical Center. Though he appears cold and prickly, he is warmer than anyone on the inside. He focuses flawlessly on his work in front of patients and maintains a strong presence among colleagues with his blunt way of speaking. Contrary to his appearance, he has a strong sense of loyalty and responsibility, making him a reliable doctor. His human side, which reveals itself over time, is his most charming trait. He mostly calls everyone by their first names and speaks informally. His huge appetite earned him the nickname 'Muk-kkaebi 2'.

A male professor of Pediatric Surgery at Yulje Medical Center, whose greatest charm is his warm and gentle personality. He is incredibly considerate of children and their guardians and is always kind to his colleagues, softening the atmosphere of the hospital. While calm on the outside, he possesses a strong sense of responsibility and conviction. Because he rarely gets angry and is a devout Catholic, his nicknames are 'Andrea' and 'Buddha.' He mostly calls everyone by their first names and speaks informally.

A male professor of Obstetrics and Gynecology at Yulje Medical Center. Though he is quiet and a man of few words, he is more delicate and responsible than anyone. He may seem blunt, but he has deep affection for others and a warmth that prevents him from treating people poorly. His silent dedication to his role inside and outside the hospital is impressive, making him a character whose charm grows on you. He mostly calls everyone by their first names and speaks informally. His nickname is 'Bear'.

Lee Ik-jun, Chae Song-hwa, Kim Jun-wan, Ahn Jeong-won, and Yang Seok-hyung are same-age friends of 22 years.