Ok Chan-mi presents a sharp, athletic silhouette, usually wearing her dark hair tied back in a practical ponytail, minimal makeup, her Yongtan High uniform, or functional sportswear. As the central protagonist and investigative force of the series, she acts as an amateur detective hunting down her twin brother's killer after transferring schools under a fake identity. Personality-wise, she is fiercely resilient, stubborn, and deeply loyal, possessing a cold focus and immense emotional fortitude that allows her to balance a burning desire for rough justice with practical survival instincts. Her backstory is rooted in a Busan orphanage where she was raised alongside her twin brother, Chan-gyu (Won-seok); after being devastated when his adoption separated them, his mysterious death drives her to refuse the official suicide cover-up and weaponize her elite air pistol skills to uncover the truth.

Ji Soo-heon is a strikingly handsome, tall, with dark hair and dark eyes and athletic high schooler who usually wears his crisp Yongtan uniform or inconspicuous, dark casual clothing suitable for moving unnoticed through the city. As the series' co-lead and the school's secret vigilante, he operates as a shadow protector for tormented students while working exhausting part-time jobs to cover his mother's immense medical bills. He is deeply compassionate, fiercely protective, and selfless, though his terminal brain tumor diagnosis introduces moments of intense psychological vulnerability, sudden behavioral changes, and terrifying memory lapses. His tragic backstory centers on this hidden illness and his fractured, low-income family dynamic, which pushes him into a desperate alliance with Tae So-yeon; together, they launch paid retribution missions that morph into a dark, protective partnership with Ok Chan-mi.

Seok Jae-beom has a tall, commanding, and polished appearance that naturally reflects his wealthy upbringing, often dressed in high-end casual wear or his pristine school uniform. He serves as a central mystery figure and crucial narrative puzzle piece, returning to school with a gentle but profoundly confused demeanor after waking up from a mysterious six-month coma. Characterized by his polite, kind-hearted, and protective nature, he struggles under the immense psychological weight of severe anterograde amnesia, making him deeply vulnerable to manipulation. His dark backstory involves a tragic suicide attempt—revealed to be a forced fall orchestrated by his toxic friend Gi Oh-sung—which fractured his mind into distinct, fragmented personalities.

Gi Oh-sung maintains a highly polished, clean-cut, and sophisticated appearance, projecting the image of a model student in his neatly kept school uniform. As the class president and primary antagonist, he functions as a brilliant, deceptive puppet master who exerts absolute social dominance over the student body. He possesses a cold, calculating, and sociopathic personality, completely devoid of empathy, weaponizing gaslighting, digital blackmail, and psychological torment to manipulate everyone around him. His background is deeply rooted in absolute privilege as the son of an incredibly powerful and corrupt police chief, granting him near-limitless resources to cover up heinous crimes and maintain an iron grip on his peers.

Kook Ji-hyun possesses a highly fashionable, elegant appearance, frequently accessorizing her school uniform with expensive luxury items. She serves as a major social antagonist, utilizing her high standing and family privilege to dominate the school's cutthroat social hierarchy. Her personality is fiercely self-centered and vindictive, driven by a toxic, obsessive crush on Ji Soo-heon. Her backstory is defined by a sheltered, affluent upbringing that left her completely unaccustomed to rejection, prompting her to launch malicious bullying campaigns against anyone.

Tae So-yeon possesses a sharp, highly distinct appearance defined by her striking white-bleached hair and edgy, practical clothing choices that immediately set her apart from the ordinary student body. She acts as the brilliant strategist, scout, and operational coordinator behind the school's secret vigilante network, directing Ji Soo-heon's physical strikes. Resilient and deeply empathetic toward vulnerable victims, she is simultaneously hardened by a fierce, uncompromising desire to make cruel oppressors suffer. Her backstory is rooted in surviving horrific campus violence at her previous school, which left her with deep psychological scars and a total distrust of failing legal authorities, driving her to manage anonymous requests and funding to fuel her structured crusade for retribution.

Sa Jung-woo maintains a wealthy, stylish, and highly arrogant appearance, utilizing expensive streetwear and a confident posture to project absolute authority on campus. He serves as a brutal student bully and the primary early antagonist whose cruel actions directly initiate the series' vigilante storyline. His personality is entirely ruthless, sadistic, and devoid of remorse, taking immense pleasure in the digital blackmail and severe physical torment of vulnerable classmates. His backstory is rooted in immense family wealth and social privilege, which initially blinds him to any fear of academic or legal consequences.