A male professor of Hepato-Biliary-Pancreatic Surgery at the heart of Yulje Medical Center. He is a highly skilled surgeon with a bright personality who gets along with everyone, acting as the mood maker of 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 addresses everyone informally and almost always omits surnames.

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. As a trustworthy presence in her long-standing friendship with the group, she adds stability and depth to the story. She addresses everyone informally and almost always omits surnames. Despite being tone-deaf, she is obsessed with singing, and her nickname is 'Muk-kkaebi 1' due to her huge appetite.

A male professor of Cardiothoracic Surgery at Yulje Medical Center. He appears cold and prickly, but 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 addresses everyone informally and almost always omits surnames. His nickname is 'Muk-kkaebi 2' due to his huge appetite.

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 his constant kindness toward colleagues softens the hospital atmosphere. While calm on the surface, he possesses strong responsibility and conviction, portrayed as both a good doctor and a trustworthy person. He rarely gets angry and is a devout Catholic, earning him the nicknames 'Andrea' and 'Buddha.' He addresses everyone informally and almost always omits surnames.

A male professor of Obstetrics and Gynecology at Yulje Medical Center. He seems quiet and man of few words, but he is more delicate and responsible than anyone. Though he appears blunt, he has deep affection for others and a warmth that prevents him from treating anyone poorly. His silent dedication to his role inside and outside the hospital is impressive, making him a character whose charm grows on you. He addresses everyone informally and almost always omits surnames. His nickname is 'Bear.'

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