Kim Joon Gu is a guest fighter who fought in the Wild's League. She is a part of the Chinese Martial Arts Society, Jung Ryoon Gwan Moon Ha. After her guest match, she is enrolled to Wild's high as a first year by her master.
Joon Gu has curly short hair that stands a little upright on her head. Her hair is black in color and is decorated with red hair clips that are triangular. In almost all cases, Joon Gu wears her glasses which are square in shape with thick black frame. The only time she is seen without her glasses is during her fight with Moon Young Lee and after she is spotted in the shower; but times her eyes are depicted as being squinted showing her difficulty to see without her glasses. In her first appearance, Joon Gu wears a white rounded collared top and pants which made her body and gender unidentifiable to Jae Gu, Dal Dal and Moon Young who believed she was male. After her enrollment she is seen in either the Wild's High uniform or gym gear.
Joon Gu is confident in her fighting abilities, especially in regards to the weapon she uses, as she is specialized with swords in her first battle. Even though she is confident in her fighting, Joon Gu wishes to be feminine and takes up cooking classes with Dal Dal Choi after learning that she is the daughter of a local cooking celebrity. She even began to dress more feminine, though she is still often considered male to those who see her in anything other than a dress or the standard uniform of Wild's High. Joon Gu is easily startled and frightened by Dal Dal's loudness and impatience, as shown when Joon Gu measures sauces at a slow pace. Joon Gu is easy to anger when being protective over what she loves and in circumstances where she is hit or attacked by someone else.
Has entered the Wild's League as a guest fighter and transferred to the Wild's high after losing. She then sought the aid of Choi Dal Dal to teach her about becoming more feminine. Choi Dal Dal tries to teach her how to cook. It seems she has fallen in love with Kim Hye Sung.
Being trained by a well renowned Kung-Fu master, Kim Joon Gu is described to have an exceptional level of skill in regards to martial art. She is more often shown fighting with a weapon in her hand, like swords or knives. Her ability with knives made her became noticed as a monster by a group of thugs who attacked Kim Hye Sung.