Kim Yeo Jung first appears alongside her fighting companion, Kim Jun Gu, as guest fighters in the Wild's High League. Her opponent in the guest match is Dal Dal Choi, whom she loses to. After her defeat, she is allowed to enter Wild's High and attend classes.
Although being female, Yeo Jung is often mistaken for being male. This is caused by her short messy black hair, pale refined face and the bulky white uniform that she first appears in. Another striking feature of Yeo Jung is the black eyeliner and red make-up she wears that highlight her narrow grey eyes. After joining Wild's High she is seen in both the standard pink gym clothing worn by students in training or the standard uniform worn by the girls in the school.
Yeo Jung is a quiet individual who often does not speak unless she is spoken to first. She is confident in her fighting abilities, but she does admit when her fighting style has weaknesses or flaws in comparison to other fighting styles. She is shown to be caring of her friends as she makes sure Jae Gu Song is not doing anything regrettable and even takes the bus home with him. She is shown to be very polite, not refusing the advances of the girls who mistake her, and does not correct them when they incorrectly called her a boy, though she did correct Dal Dal after joining Wild's High. She has an odd sense of humour as she finds the notes the girls leave her in attempts of hitting on her a good read at night, even offering Jae Gu some to make him laugh. In chapters 183,184 and 185, more of her character is revealed, (in the conversation with Jaegu) where she is shown as a person who is wise, disciplined and a good adviser. She is also very straight forward, unlike other ordinary girls, where she tells Gangrok that he is cute and immediately offers him half of the coffee that she had been drinking and asks him to give her his number while drinking it and then she leaves. This is a possible ship between Gangrok and Yeo Jung.
Yeo Jung, alongside Kim Joon Gu, later transfer to Wild's High as first year students after competing in the guest match against Dal Dal and Moon Young Lee. As their master is currently leaving to go to China, he wishes to enroll them into Wild's High, using their matches against Dal Dal and Moon Young as an insight and exam for enrolling them into the academy. After they are enrolled, they meet up with Dal Dal and Jae Gu, who are shocked to learn that both of them are female. Yeo Jung is then later seen traveling on the bus, after seeing Jae Gu entering Goo Ra High's gym, she followed him in and observes him fighting against Kim Hye Shin. She then asks Jae Gu why he is at the Goo Ra High Gym and after learning that he wishes to get training tips for Moon Young and Dal Dal to use when coaching them. She offers some assistance before Li Mi Nam asks her would she like to have a trial match with him. Believing that she can beat Li Mi Nam she takes him up on his offer but loses to him. On the bus back home both her and a badly beaten Jae Gu sit on a bus talking about the matches. Jae Gu was given notes meant for her, he passes them over while asking about them. She then informs Jae Gu about the amount of notes she receives and then offers Jae Gu some as a good read if he ever needs one.
They are both part of the Chinese Martial Arts Society, Jung Ryoon Gwan Moon Ha, and specialize in weapon-based combat. However, Yeo Jung is more than adept with hand-to-hand combat and doesn't hesitate to fight back when necessary, a trait shown when she fights Mi Nam completely unarmed and almost defeats him.