Choi Kang Rok is a 9th grader who is saved by, and devoted to, Song Jae Gu. He plans to enter Wild's High with the aim of becoming as strong as Jae Gu.
Choi Kang Rok has a feminine face, is shorter than the average boy of his age, and possesses a skinny and frail body. Choi Dal Dal noted that he does not have a good bone structure and because of this, he cannot become "strong". His hair is a dark brown and well kept with only his fringe being parted in three ways. His eyes are a chestnut brown and quite large which makes him have such a feminine face/ His normal attire consists of his school uniform; a maroon colored jacket over a maroon sweater with a white shirt, red tie tucked under his sweater and black slacks. When training Kang Rok wears a white sleeveless jacket which is zipped up and yellow and white tracksuit bottoms.
Choi Kang Rok has a desire to be strong so that the others will stop bullying him. Because of this, he follows Jae Gu around and begs the elder boy to train him despite the fact that Jae Gu himself is a mere beginner. He is known to be quite sensitive as he is shown crying when he was told by Dal Dal that he cannot become strong due to problems considering his physique.
Choi Kang Rok calls Song Jae Gu "hyung" which mean "big brother", showing that he look up to him as a big brother and sees him as someone who understand his situation and why he wants to be strong. When Moon Young is fighting on behalf of Kang Rok, he becomes apologetic towards her, feeling that she should not be fighting for him. He is often portrayed as apologetic and filled with self doubt when being bullied or criticized. However he shows determination and persistence in wanting to change his flaws and turn them intro strengths so that he can enroll into Wild's High and become as strong as Jae Gu.
In his middle school, Kang Rok is bullied by several other students of his school. At one point he is spotted by Jae Gu who fights off the bullies before offering help towards him. Inspired by Jae Gu's strength and similar story he vows to become stronger asking the elder man to train him not caring that Jae Gu is not an experienced fighter. It is later learned that he is ranked third in terms of grades in his school, a feat which is hard to achieve.
Kang Rok is considered highly intelligent in terms of academic studies. In regards to fighting he has yet to prove his capabilities but has shown progression in his work-outs since he first started training