Weak hero

Sung Jae (Geum Sung Jae) is Baek Jin's right-hand man, efficient and strict. He doesn't so much come up with plans as he implements them, strictly following the leader's line. A practical man who doesn't ask unnecessary questions.

Baek Jin (Na Baek Jin) is smart, calculating, and ruthless; he gathers an "Alliance" around himself and plays by adult rules. He uses the school as a platform to build power and even launder money for gangs. He combines intelligence with cruelty and has no inhibitions. He is the leader of the "Union" gang, which includes many schools.

Joon-tae (Seo Joon-tae) is a downtrodden, insecure boy who initially just wants to stop being bullied. He falls into Shi-eun's orbit, learns to stand up for himself, and gradually finds his voice—a typical outsider finding a place in a new group.

Gotak (Hyuntak Go) is a former taekwondo athlete whose career was cut short by an injury. Now he's a pillar of support for his team: reliable, quiet, and keeps his word and punches. He often acts as a "shield" for those he trusts.

Hu Min (Park Hu Min) is affiliated with the Alliance, but doesn't blindly follow the rules: he knows how to hold his own and isn't afraid to go against the grain. He acts prudently, but is not without principles—in some ways, a counterweight to outright villains. He's cheerful and sociable.

Young Bin (Jeon Young Bin) is the school's elementary-level "boss," accustomed to using force and terrorizing the class. He's confident in his superiority until he encounters Suho and receives a brutal rebuff, after which his position noticeably falters.

Beom-seok (Oh Beom-seok), the son of a councilman, is torn between his desire to be strong and his fear of becoming a victim again. Initially, he reaches out to Shi-eun and Su-ho as those who can protect him, but envy and insecurities gradually push him to betrayal. One of the most tragic characters, he transforms from victim to aggressor.

Suho (Ahn Soo-ho) is a fighter with a background in MMA, honest, straightforward, and with a strong sense of justice. He becomes Shi-eun's support and protector, while trying to avoid fights himself out of a promise to his grandmother that he'll graduate safely. He's extremely loyal to his friends—and it's this loyalty that makes him especially vulnerable.

Shi-eun (Yeon Si-eun) is the protagonist, a quiet, straight-A student on the outside, but a cold-blooded strategist in reality. While physically weak, he's adept at predicting his opponents and using his knowledge and available items as weapons. His motivation is first to simply survive school, then to protect those he's come to care about.