Gu Do-won

A 4th-year OB/GYN resident. He is a Superman to the new residents, appearing whenever trouble arises and vanishing just as quickly, but in reality, he is just an ordinary resident who practically lives at the hospital. He is related to Oh I-young by marriage and calls her 'Sister-in-law.'

Seo Jung-min

Chief and Professor of Obstetrics. She possesses a 'sweet and salty' charm, acting like a wicked witch in March but becoming the 'Professor of the Year' voted by residents by December. She is serious during surgery but cool enough to give praise where it's due.

Gong Gi-seon

Professor of Obstetrics. The OB/GYN residents check his mood the moment they arrive at work. On good days, he arrives with a high-pitched voice and takes care of the residents' breakfast; on bad days, he suddenly explodes over things he said were fine yesterday. His nickname is Amadeus the Devil.

Jo Jun-mo

While Professors Seo Jung-min and Gong Gi-seon trust Oh I-young deeply, Jo Jun-mo tends to pick on her and give her a hard time.

Oh Ju-young

A housewife, Oh I-young's older sister, and Gu Do-won's sister-in-law. She is 11 years older than I-young. She is the only person who can suppress the wild and fearless I-young with just a single look. Since their parents passed away while she was in college, she has been acting as a mother figure to I-young.

Gu Seung-won

An IT company researcher, Gu Do-won's older brother, and Oh I-young's brother-in-law. He is also Oh Ju-young's husband. A devoted romantic who can gauge Ju-young's mood just by the sound of her breathing and catch the hidden meaning in the number of periods in her texts.