Yoo Jae-yi

Face: delicate and proportionate, with soft but quite defined features.
Eyes: Large and expressive, usually with a calm and confident gaze. They can easily change from a friendly expression to a colder or more calculating one.
Eyebrows: well-defined and natural, which help to give a serious expression when he is not smiling.
Nose: thin and proportionate to the face.
Lips: defined, generally with a discreet and elegant expression.
Hair: dark, long and straight, usually worn in a simple and neat manner.
Skin: clear and well-cared for.
Body type: slim and slender, with a very straight and elegant posture.
Style: She usually dresses impeccably, with her uniform perfectly groomed. Her appearance conveys a sense of a wealthy, sophisticated, and self-assured young woman.
Presence: perhaps her most distinctive feature is that she doesn't need to make grand gestures to attract attention. The way she looks, walks, and remains calm makes it seem as if she is in control of the situation.

Very intelligent: she is Chaehwa's number one student and is used to excelling academically.
Wikipedia
Self-assured: she knows perfectly well that she has influence, talent and a privileged position, and she rarely doubts her abilities.
Elegant and composed: she almost always maintains a calm expression and impeccable demeanor. It's difficult to know what she's really thinking.
Astute: She analyzes people and situations before acting. She also knows how to use her social position to get what she wants.
AsianWiki
Competitive: She is used to winning and may consider other people as obstacles when she feels they threaten her position.
Manipulative: She can appear extremely kind while keeping her true intentions hidden. Her kindness doesn't always mean she's acting out of pure goodness.
Soompi
Emotionally reserved: she doesn't usually say what she feels directly. She prefers to hide her emotions behind a smile, a look, or a seemingly indifferent attitude.
Cold at times: when something doesn't matter to her, she can be surprisingly distant.
Proud: She is not used to being rejected or losing control of a situation.
Protective of someone she truly cares about: her relationship with Seul-gi shows that, although she may initially approach someone for self-serving reasons, her feelings can become more genuine over time.