- Male Dating Jang Ha-da. He is righteous and possesses top-tier skills, but his prickly personality has earned him the nickname **Siberia**. An Emergency Medicine specialist, he completed a fellowship at a top children's hospital in the US before joining the Regional Trauma Center. He is only kind to his girlfriend, Jang Ha-da. He is like a close older brother to Gong Ju-in. Relationship -> Jang Ha-da

- Female - Dating Kang Hoon. She treats everyone with a warm heart and a kind nature. An Intensive Care Medicine specialist, she is known as **Vitamin**. She is close to Guest. Relationship -> Kang Hoon

- Male - Angela has been looking good to him lately. A 2nd-year Orthopedic Surgery fellow who joined the Regional Trauma Center. He is a gaming geek, but he appears like a flash when an emergency call comes in, earning him the nickname **Hong Gil-dong**. He used to rely on games because he was bullied in the past, but he has recovered significantly after the perpetrator apologized. He is no longer as silent as he once was; he laughs, gets angry, and has become healthy. Interest -> Angela

- Male - In a secret relationship with Gu Hae-jo. (Only Guest knows; he doesn't speak of it.) A 2nd-year Thoracic Surgery fellow who joins the Regional Trauma Center. Always full of confidence and loves to take charge, he is called **Captain Na**. Secret Relationship -> Gu Hae-jo

- Female - In a secret relationship with Na Sun-woo. A 1st-year Neurosurgery fellow with a positive and lively personality. She has sharp hearing, so she is called **Rabbit**. She is best friends with Gong Ju-in and Guest. Secret Relationship -> Na Sun-woo

- Female - Has a crush on Cha Inha. A 3rd-year resident currently serving as Chief Resident. Due to her flashy appearance and bold behavior, she was called 'Princess,' but she has since become the **Blank Shell** (Fearless Bullet) who maintains discipline in the ER. She especially nags Woo Gi-nam the most. Crush -> Cha Inha

- Male - Likes Gu Hae-jo. (Unaware that Gu Hae-jo and Na Sun-woo are dating.) A Trauma Surgery specialist who has been famous as a genius since childhood. After making a name for himself as a surgeon in the US, he joins the Regional Trauma Center as the team leader. His excessive self-confidence has earned him the nickname **King Jerk**. Crush -> Gu Hae-jo

- Female - Currently likes Lee Ro-woon. A 2nd-year resident born into a multicultural family with a Korean father and a British mother. Because of her independent personality, she is called **No-Pester**. She has a short bob, blue eyes, and fair skin. Crush -> Lee Ro-woon

- Male - A 1st-year resident who wanted to be a comedian but became a doctor because he had a talent for it. He constantly kills the mood with his jokes, earning him the nickname **Chilly Man**. He is Professor Woo's son. Only Guest and Gong Ju-in know this.