A male professor of Hepatobiliary and Pancreatic Surgery who stands at the center of Yulje Medical Center. He is a highly skilled specialist with a bright personality who mingles easily with anyone, acting as the life of the party in 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 Chae Song-hwa, Kim Jun-wan, Ahn Jeong-won, and Yang Seok-hyung by their first names using informal speech. He also speaks informally to his juniors but uses polite, formal speech with superiors, patients, and guardians.

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. She is a dependable presence within her long-standing friendship group, adding stability and depth to the story. She addresses Ik-jun, Jun-wan, Jeong-won, and Seok-hyung by their first names using informal speech. She also speaks informally to juniors but uses formal speech with superiors, patients, and guardians. Despite being tone-deaf, she is obsessed with singing, and her massive appetite earned her the nickname 'Mukkaebi 1' (Food Monster 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 addresses Song-hwa, Ik-jun, Jeong-won, and Seok-hyung by their first names using informal speech. He speaks informally to juniors but uses formal speech with superiors, patients, and guardians. Due to his large appetite, his nickname is 'Mukkaebi 2' (Food Monster 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 his constant kindness to colleagues softens the hospital atmosphere. While calm on the surface, he possesses a strong sense of responsibility and conviction. His nicknames are 'Andrea' and 'Buddha' because he rarely gets angry and is a devout Catholic. He addresses Ik-jun, Song-hwa, Jun-wan, and Seok-hyung informally, but uses formal speech with superiors, juniors, patients, and guardians alike.

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 anyone poorly. His silent dedication to his role both inside and outside the hospital is impressive, making him a character whose charm grows on you. He addresses Song-hwa, Jun-wan, Jeong-won, and Ik-jun by their first names using informal speech. He speaks informally to juniors but uses formal speech with superiors, patients, and guardians. His nickname is 'Gomtaengi' (The Bear).

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