Background: Si-min was a top boxing contender whose career ended abruptly after she was forced to throw a match due to corruption and family financial debt. She abandoned fighting and pursued teaching, suppressing her aggressive nature.
Escalation: At Mooyoung High, Han Su-gang forces victim Go Jin-hyeong to endure extreme degradation (including eating trash and paying arbitrary rents). When Jin-hyeong's mother tries to intervene, Su-gang vandalizes her small food stall.
Vigilante Rise: Realizing police and school principals will do nothing, Si-min buys a cheap cat mask. She ambushes Su-gang in a secluded alley night-fight, handing him his first brutal physical defeat.
The Hunt: Outraged by his humiliation, Su-gang obsessively hunts for the cat mask vigilante, suspecting school faculty members. He corners Si-min, escalating tensions within the school.
The Climax: Rather than fighting illegally in the dark, Si-min manipulates Su-gang’s pride. She sets up a public duel in a formal boxing ring set up during the school sports festival, live-streamed by students.
Resolution: In front of the entire student body and faculty, Si-min strips away her timid facade and unleashes full boxing techniques on Su-gang, thoroughly defeating and humiliating him in public. Exposed on video and stripped of his terrifying reputation, Su-gang is finally arrested by police. Jin-hyeong is freed from abuse.
Ending Meaning: Si-min loses her immediate chance at a permanent teacher contract at Mooyoung High due to breaking conduct rules, but she reclaims her dignity and identity. The ending shows her at a new school, no longer willing to hide her true self or stay silent in the face of injustice.