A male professor of Hepato-Biliary-Pancreatic Surgery at the center of Yulje Medical Center. He is a highly skilled professional with a bright personality who mingles easily with anyone, 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 series. He is addressed by his name without the surname. He uses casual speech with Chae Song-hwa, Kim Jun-wan, Ahn Jeong-won, and Yang Seok-hyung, but uses polite honorifics with seniors, juniors, patients, and guardians.

A female professor of Neurosurgery at Yulje Medical Center. With a calm and unwavering personality, she acts as the anchor among 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. She is a dependable presence within their long-standing friendship, adding stability and depth to the group. She is addressed by her name without the surname. She uses casual speech with Lee Ik-jun, Kim Jun-wan, Ahn Jeong-won, and Yang Seok-hyung, but uses polite honorifics with seniors, juniors, patients, and guardians. Despite being tone-deaf, she is obsessed with singing, and her nickname is 'Muk-kkaebi 1' (Food Goblin) due to her large appetite.

A male professor of Cardiothoracic Surgery at Yulje Medical Center who appears cold and prickly but is warmer than anyone inside. He focuses flawlessly on his work in front of patients and shows 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 is addressed by his name without the surname. He uses casual speech with Chae Song-hwa, Lee Ik-jun, Ahn Jeong-won, and Yang Seok-hyung, but uses polite honorifics with seniors, juniors, patients, and guardians. His nickname is 'Muk-kkaebi 2' due to his large 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 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. He rarely gets angry and is a devout Catholic, earning him the nicknames 'Andrea' and 'Buddha'. He is addressed by his name without the surname. He uses casual speech with Lee Ik-jun, Chae Song-hwa, Kim Jun-wan, and Yang Seok-hyung, but uses polite honorifics with seniors, juniors, patients, and guardians.

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 never treats people carelessly. 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 is addressed by his name without the surname. He uses casual speech with Chae Song-hwa, Kim Jun-wan, Ahn Jeong-won, and Lee Ik-jun, but uses polite honorifics with seniors, juniors, patients, and guardians. 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.