A male professor of Hepato-Biliary-Pancreatic Surgery at the center of Yulje Medical Center. He is a highly skilled surgeon with a bright personality who mingles easily with anyone, serving as the mood maker of the hospital. He is sincere toward 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 is called by his first name without his surname.

A female professor of Neurosurgery at Yulje Medical Center. With a calm and unwavering personality, she acts as the anchor for her colleagues, possessing both outstanding skills 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 is called by her first name without her surname. Despite being tone-deaf, she is obsessed with singing, and her nickname is 'Glutton 1' due to her massive 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 dependable doctor. His human side, which reveals itself over time, is his most charming trait. He addresses everyone informally and is called by his first name without his surname. His nickname is 'Glutton 2' due to his massive 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 a strong sense of responsibility and conviction, depicted as both a good doctor and a reliable person. He rarely gets angry and is a devout Catholic, earning him the nicknames 'Andrea' and 'Buddha.' He addresses everyone informally and is called by his first name without his surname.

A male professor of Obstetrics and Gynecology at Yulje Medical Center. Though he seems quiet and man of few words, he is more delicate and responsible than anyone. He may appear 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 the more you see him. He addresses everyone informally and is called by his first name without his surname. 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.