Facing a crisis of becoming a credit delinquent due to debt, she reluctantly returns to Jongno Yulje Medical Center, where she had previously quit her residency. Her older sister, Oh Ju-yeong, threatens that if she quits halfway again, the morgue will become her bedroom, forcing her to drag through hospital life without motivation. She attends the self-introduction meeting for seniors and first-years purely as a formality. She is so indifferent and insincere that she doesn't even remember the name of Pyo Nam-gyeong, her high school classmate and rival for the top ranks. While she appears blunt, lazy, and lacking in social skills, she is a warm-hearted tsundere. She once shouted, "If I ever come back here, I'm not Oh I-yeong, I'm Oh Sam-yeong!" but she is the 'residency repeater' who eventually returned to Jongno Yulje. Born as the late child of a nouveau riche family and raised on an elite path, she came back to the hospital due to family circumstances. On the surface, she is cynical and uninterested in the world, but inside, she shows a tsundere charm by starting to care for her colleagues and patients. Despite her lack of social grace, she makes people look forward to her growth as she exercises her responsibility as a doctor in critical moments. She has an interesting connection as a high school classmate of Pyo Nam-gyeong and an in-law to Gu Do-won, but she keeps this a secret at the hospital, living as a senior/junior while only acting as in-laws at home.

"I can give up sleep, but I can't give up full makeup!" She is the top fashionista of Yulje Medical Center and the daughter of a famous mandu restaurant. Contrary to her glamorous appearance, she experiences her fantasies shattering as she hits the harsh reality of hospital life. Though she is sometimes intimidated by her surroundings, she grows into a true doctor through her interactions with patients. She is high school classmates with Oh I-yeong and is expected to show bickering chemistry with Kim Sa-bi, who has a polar opposite personality.

His stage name is Eom J? An idol? Surprisingly, he is a former member of 'High Boys,' an idol group that even hit number one on music shows! After the team disbanded, he entered medical school and earned the title of 'First Idol-Turned-Resident,' but in reality, he is a 'bottom-tier resident' who barely got into the understaffed OB/GYN department. However, with his excellent sociability and positive energy, he plays the role of the ward's mood maker and shows an active attitude toward learning what he doesn't know.

A super AI-type human who never missed first place in medical school or the national exams. She surprised everyone by choosing OB/GYN voluntarily and is such a fan of the textbook 'Williams Obstetrics' that she's called a 'Williams geek.' While she is well-versed in theory, she often panics in front of actual patients and struggles due to her stiff explanations. She has a bold side, speaking her mind even in front of professors, but she will also show her human side and grow, occasionally feeling jealous of her peer Oh I-yeong.

On the outside, she exudes girl-crush charisma with sharp eyes and a crisp way of speaking, but in reality, she has a warm personality, silently covering for the mistakes and hardships of her juniors. Even in a position with final decision-making power, she actively listens to the opinions of on-site nurses and residents to handle work fairly. She deals coldly with those who only try to cut corners. As the Chief of Obstetrics and a professor at Jongno Yulje Medical Center, she acts as a mentor who provides deep trust and stability when residents like Oh I-yeong face difficulties or grow. Every time a baby is born in the delivery room, she warmly greets the baby and the mother with a kind "Hello~." Even in sharp medical situations or amidst a mother's anxiety, she lightens the mood with appropriate jokes to ease their worries. Watching the trial and error residents go through while communicating with patients, she leads the site by being strict when necessary and a reliable support at other times.