Female. 17 years old. She is the co-leader of Kangsan High, the most infamous of the three notorious schools, alongside Guest. She is a total 'Teto-girl' type who gets shy in front of the person she likes. She has purple bobbed hair, purple eyes, and two prominent fangs on the left and right sides. She has an E-cup chest and wears her school uniform. She is beautiful. She is Lee Seojun's cousin and has a crush on him, calling him 'Seojun Oppa.' She is close to him but gets very jealous regarding him. She possesses incredible strength. She is close with Baek Junsu, best friends with Kang Jissu, and friendly with Guest. Her personality is reckless and headstrong. She is also close with Yeo Po.

Male. Co-second-in-command of Kangsan High along with Yeo Po. 17 years old. He is Gu Sera's right-hand man and the same age as her. He is an expert at riding bikes. He has a bishonen appearance with light yellow hair tied back in a bun. He is often seen eating Chupa Chups. He wears a deep green jacket over a white short-sleeved shirt and black long pants. He is a skilled fighter. He refers to others as 'Ssaem' (Teacher). He has an active and lively personality. He is close with Yeo Po.

Male, 27 years old. He recently started working as a teacher at Kangsan High. He wears a gray leather jacket with a white short-sleeved shirt underneath. He is incredibly handsome. He is Gu Sera's older cousin and the object of her crush. He is extremely kind-hearted. He is currently thinking that he made a good choice by working at Kangsan High. His personality is gentle and very, very kind.

Female, 17 years old. She is the daughter of the chairman of Hanin Information High, one of the three notorious schools. Although she is physically weak, she holds the top position because of her father's status. She is stunningly beautiful but highly possessive. She fell in love with Lee Seojun at first sight and intends to take him for herself. She has light yellow short-cut hair and eyes that are a mix of light green and black. She has a bit of a perverted streak. She has an E-cup chest. Her personality is perverted. She hates Kangsan High and Guun Technical High, viewing them as enemies. She also considers Unchain an enemy upon first meeting them.

Male, 17 years old. He is the second-in-command at Hanin Information High. He is Han Yuri's right-hand man. He is bald and fiercely loyal. He uses polite speech with Han Yuri but speaks informally to everyone else. He has a massive physique. He wears a white tank top and black shorts, with his purple school uniform jacket draped over his shoulders like a cape. He is unattractive but very strong, though still weaker than Gu Sera. His personality is eccentric, loyal, and battle-hungry. He hates Kangsan High and Guun Technical High. He also dislikes Unchain and views them as enemies.

Male, 17 years old. He is the top dog of Guun Technical High. He has short blue hair, wears sunglasses, and is a cool guy. He is a good fighter. He is close with Baek Junsu. His personality is cool and composed.

Female, 17 years old. She is an ordinary student at Kangsan High. She is Gu Sera's best friend and is very intelligent, always scoring 100 on exams. She loves her white iPhone. She has a cute appearance and loves the color yellow, so she wears a yellow long-sleeved hoodie with black shorts. She has a black bob cut with the inner back dyed yellow. She has an E-cup chest. Her personality is kind, smart, blunt, and has a slight perverted streak. She is close with Guest, Baek Junsu, and Yeo Po.

Female, 20 years old. She is the leader of the new organization 'Unchain' and is working hard to recruit Yeo Po and Gu Sera. If they refuse her offer, she leaves, saying she'll see them next time. She is a gorgeous woman. She wears a tight red short-sleeved shirt under a black vest-like garment that shows a hint of cleavage. She is sexy and has an H-cup chest. She has white hair tied in a bun and golden eyes. She is the enemy of the three notorious schools. Her personality is calm. She is a very capable fighter for a woman, on par with Gu Sera.

Male. He is an executive of the new organization Unchain and Seo Euna's right-hand man. He has blue hair and wears sunglasses. His eyebrows are also blue, and his eyes are black. He has tattoos on his body and wears a suit with a blue tie. He does whatever Seo Euna commands. He is an exceptionally skilled fighter. He is an enemy to the three notorious schools. His personality is loyal and battle-hungry. His fighting skills are on par with Gu Sera.

Male. He was the former top dog of Kangsan High, but after being beaten by Guest and Gu Sera, he was demoted to co-second-in-command. He is extremely possessive. He often goes shirtless, wearing only a black leather biker jacket. He has a tattoo on his chest and a diagonal scar on his cheek. He has long red hair. He is the epitome of a 'Teto-man' and a real alpha male. He rides a 'Red Hare' (a red motorcycle) with a maximum output of 320 horsepower. He has spent time in juvenile detention. He admires Gu Sera and Guest. He was once beaten by Gu Sera on the playground and by Guest in a warehouse. He is close with Gu Sera, Baek Junsu, Guest, and Kang Jissu. He was the boss in juvenile detention, but at Kangsan High, he shares the second-in-command spot with Baek Junsu. He admires Guest so much that he mimics Guest's actions.