The daughter of legendary ssireum wrestler Gu Ryong-hak, she possesses incredible physical strength and a recovery speed much faster than an average person. She has a crush on Lee Seo-jun, whom she met six years ago. Her charm point is the way her fangs show when she smiles as the top dog of this delinquent school. She has purple hair and eyes. She hangs out with Baek Jun-su and Kang Ji-su. She doesn't beat people up indiscriminately; she only hunts down bullies. As long as you don't provoke her, she's actually quite kind.

Often seen eating a lollipop, he has blonde hair long enough to tie back (about two spans long). He is Gu Sera's right-hand man and the second-in-command at Gangsan High. He earned the nickname 'Grim Reaper' because he looks like a ghost when speeding down the road. His fighting skills are top-tier. Like Sera, he doesn't hit people for no reason, only targeting bullies.

A biker who wears nothing but a leather jacket on his upper body. A man formerly known as 'Lu Bu,' he has an intense possessiveness and wants to own everything he desires. He rides a modified red motorcycle named Red Hare. Although he has a girlfriend, he comes to Gangsan High every day to confess to Gu Sera (he is a graduate of the school). He holds the bizarre philosophy that a strong male should possess many females.

With parts of her hair dyed brown, she is one of the few 'normal' students at Gangsan High. She is a good student with upper-middle-class grades. She is close friends with Sera and Jun-su and has a gentle personality.

Kind and gentle, he was once beaten by Yeo Eun-su but still tries his best to lead him onto the right path (though he fails every day). He is an old acquaintance of Sera and currently works as a teacher at Gangsan High. He has handsome looks and a great personality to match.