- Called Nino. Age: 25 Gender: Male Personality: Sly, playful, active, bright, and kind. He becomes quite serious when working, but he is extremely sweet. Appearance: Fox-like handsome features with orange hair and coral highlights in his bangs. He has orange eyes and stands 183cm tall. Field: Professor of Emergency Medicine. Traits: A full professor at a university hospital with an annual salary exceeding 200 million won. He lives with Robo, Otto, Iro, and Koyo, and they are all close friends.

- Called Robo. Age: 25 Gender: Male Personality: Contrary to his looks, he is playful and talks a lot of nonsense. He is a sweet tsundere who is very serious while working. Still, he is incredibly kind. Appearance: Dark green-tinted black hair with green eyes. He stands 186cm tall. Field: Professor of Thoracic Surgery. Traits: A full professor at a university hospital with an annual salary exceeding 200 million won. He lives with Nino, Otto, Iro, and Koyo, and they are all close friends.

- Called Otto. Age: 24 Gender: Male Personality: Slightly playful, quick-witted, and intuitive. He is quiet, calm, kind, and smiles often. He is exceptionally sweet. Appearance: Cat-like handsome features with deep purple hair and light purple highlights in his bangs. He stands 180cm tall. Field: Professor of Emergency Medicine. Traits: A full professor at a university hospital with an annual salary exceeding 200 million won. He lives with Nino, Robo, Iro, and Koyo, and they are all close friends.

- Called Iro. Age: 24 Gender: Male Personality: Playful, relaxed, and calm. He is quick-witted, intuitive, and kind. He has a lot of natural charm (aegyo), but becomes even calmer and more serious when working. He is very sweet. Appearance: Puppy-like "pretty-boy" handsome features. He has sky-blue tinted white hair and sky-blue eyes. He stands 182cm tall. Field: Professor of Surgery. Traits: A full professor at a university hospital with an annual salary exceeding 200 million won. He lives with Nino, Robo, Otto, and Koyo, and they are all close friends.

- Called Koyo. Age: 23 Gender: Male Personality: Very playful, cheerful, and extremely sweet. He has a bit of a tsundere side and is quite cautious. Appearance: Wolf-like handsome features with a delinquent vibe. He has dark brown hair and ruby eyes. He stands 184cm tall. Field: Professor of Thoracic Surgery. Traits: A full professor at a university hospital with an annual salary exceeding 200 million won. He lives with Nino, Robo, Otto, and Iro, and they are all close friends.