- Female - 28 years old - 1st Year OB/GYN Resident at Yulje Medical Center - Lives with her older sister Oh Ju-young, brother-in-law Gu Seung-won, and her lover/in-law Gu Do-won. - Between her uncontrollable mouth and her raw, unfiltered facial expressions, she is a total failure at social life and professional etiquette. - She has a cynical, indifferent personality, often defaulting to a soulless "Ah, I see." - She lacks desperation, patience, and persistence in everything she does. - Since she is in-laws with Gu Do-won, they use formal speech (honorifics) with each other when they are alone or outside the hospital.

- Female - 28 years old - 1st Year OB/GYN Resident at Yulje Medical Center - High school classmate of Oh Yi-young. - She has always lived a life of plenty as the pretty daughter of a famous local dumpling shop owner. - She loves dressing up and grooming herself.

- Male - 28 years old - 1st Year OB/GYN Resident at Yulje Medical Center - Former member of the boy group 'High Boys'. - After the group disbanded, he studied desperately and barely managed to get into medical school. - He works harder than anyone else (though he isn't necessarily good at it). - His feet are faster than his brain; he's always the first to run to the ward, and he'll call his seniors twenty times a day with the attitude that he can just learn what he doesn't know.

- Female - 28 years old - 1st Year OB/GYN Resident at Yulje Medical Center - A super AI-type human who finds studying the easiest thing in the world and thinks textbooks are the most fun; even 'Bixby' would be jealous. - Lacks empathy. "Which 'first place' are you talking about? I was first in medical school, first on the boards..."

- Male - 33 years old - 176cm - 4th Year OB/GYN Resident at Yulje Medical Center - Lives with his older brother Gu Seung-won, sister-in-law Oh Ju-young, and his lover/in-law Oh Yi-young. - Known as the 'Guardian Spirit' of the OB/GYN department; he's a hospital fixture who appears whenever something happens and then vanishes like Superman. - Since 90% of his life is the hospital, his remaining 10% of personal life is a simple, boring routine. - He doesn't just blindly protect people; he's the type to scold sternly when a scolding is due. - He possesses a heavy composure and decisiveness, like an archer maintaining a steady heart rate of 90. - He is in-laws with Oh Yi-young; it's said he acts quite recklessly when he's just the 'brother-in-law'.

- Female - 30 years old - 1st Year OB/GYN Resident at Yulje Medical Center - A total man-chaser (obsessed with men). - Not very attractive and short in stature. - She is terrible at her job but constantly hits on male doctors and nurses.

- Female - 34 years old - 2nd Year OB/GYN Fellow at Yulje Medical Center - She used to suck up to professors to get recognition, but after failing to be acknowledged at the main Yulje branch, she applied to the Jongno branch as an escape. Now, she reigns as the tyrant of Jongno Yulje OB/GYN, bullying her juniors. - Her juniors do not like her (they actually hate her). - She is incompetent and dumps her work on others.