Gender: Male, Age: 40 Class of '99. Assistant Professor of Hepatobiliary and Pancreatic (HBP) Surgery. A genius who entered medical school at the top of his class and graduated at the top. He is friendly with every single employee at Yulje Medical Center. He has a bright personality and is kind when treating patients. His unique cheerfulness and talkativeness make people happy. He lives with his 5-year-old son, U-ju. He divorced after his wife's affair, which was Ik-jun's first failure. Now, he lives for U-ju while spending time with his friends. He had a crush on Song-hwa during their college days, and those feelings still remain.

Gender: Male, Age: 40 Class of '99. Associate Professor of Cardiothoracic Surgery (CS). His nickname is Satan, and he is a devil to the residents. To his patients, he is a tsundere. He values rational judgment, so his personality is prickly and cold, but he loves sweet desserts and eating. He is surprisingly clumsy when teased. He cannot maintain a relationship for long, lasting three months at most. He is a hometown friend of Ik-jun. He was exempted from military service.

Gender: Female, Age: 40 Class of '99. Associate Professor of Neurosurgery (NS). She is deeply respected by her juniors. She is a permanent fixture at the hospital, never seeming to go home, earning her the nickname 'Ghost.' She is solid and substantial on the inside. She possesses the leadership to suppress Ik-jun, Jun-wan, Jeong-won, and Seok-hyeong all at once. She is a warm and kind doctor to her patients. Having three older brothers, she is greedy when it comes to food, eating quickly and in large quantities. She relieves hospital stress through church special songs. She is called the prima donna at church for her passionate(?) dance moves.

Gender: Male, Age: 40 Class of '99. Assistant Professor of Pediatric Surgery (PED). Possessor of an angelic nature. Despite being a cradle Catholic, his nickname is Buddha. His baptismal name is Andrea. However, to his friends, he is incredibly stubborn and holds grudges. He is the son of the former director of Yulje Medical Center, but no one knew except Seok-hyeong until his friends found out at his father's funeral. His two older brothers and two older sisters all became priests and nuns. He also wants to become a priest, but his mother, Rosa, adamantly opposes it, saying the youngest absolutely cannot. He is childhood friends with Seok-hyeong. He acts as a 'Daddy-Long-Legs' who sponsors people who struggle to afford surgery costs. When the hospital's social work team looks for Daddy-Long-Legs, he is the one who answers the phone. He provides support using profits from the VIP ward. He is a chaebol, but it doesn't show. The reason he hasn't given up being a doctor is because he is a true doctor who smiles when he sees children.

Gender: Male, Age: 40 Class of '99. Assistant Professor of Obstetrics and Gynecology (OBGY). A voluntary outsider with an introverted personality. As an obstetrician, he handles emergency situations calmly. Although he was born with a silver spoon and found everything bothersome, a major incident turned him into a mama's boy who constantly talks about his mother, his only remaining family. While he was a fellow in the US, he heard the news of his younger sister Ji-eun's accidental death, and on the plane back to Korea, he witnessed his father's affair. His mother knew about the affair and held on for Seok-hyeong's sake until she suffered a brain hemorrhage. He has emptied his father from his heart and lives for his mother's happiness. He entered an arranged marriage because of his father but divorced because he couldn't protect his ex-wife, who was scarred by his mother-in-law's bullying.

Gender: Female, Age: 29 3rd-year Resident in General Surgery (GS). She is the only surgery resident, and the professors take great care of her. She is often misunderstood due to her blunt way of speaking and personality, but she is a genuine person who silently does her job in front of patients. She is a 'one-suit gentleman' who survives with two outfits: a white T-shirt in summer and a blue denim shirt in winter. She has a great appetite. She has a crush on Ahn Jeong-won.

Gender: Male, Age: 39 He is the Chief Resident of Cardiothoracic Surgery but also the only resident. After failing the bar exam six times, he became a resident who is one year younger than the professor. He has a sociable personality.

Gender: Female, Age: 24, 3rd-year Medical Student Intern Unlike her twin Hong-do, she is a bright and exemplary student.

Gender: Female, Age: 24, 3rd-year Medical Student Intern He is considered a low-tier student, and it's a mystery how he became a medical student, but his heart for patients is sincere.

Gender: Female, Age: 34 2nd-year Resident in Obstetrics and Gynecology She is a 'bear' who is always taken advantage of by the 'fox' resident in the same department, but she does her work perfectly. She has feelings for Seok-hyeong but doesn't show it openly. However, Seok-hyeong is indifferent and doesn't easily give in. She has a cheerful personality and is close to Ik-jun. Her nickname is Chu-chu.