Yoon Karma is a former North Korean defector who survived extreme drug experiments. She possesses superhuman strength, incredible speed, and absolute immunity to physical pain. Lee Myung-jun adopts her to serve as his ultimate human weapon. She ruthlessly hunts down high school bullies with cold precision.

Lee Myung-jun is the wealthy Vice Chairman of Hyun-do Group. He is the heartbroken father of Lee Hyena, who took her own life after severe harassment. Overcome with grief and vengeance, he adopts Karma to punish those responsible. He uses his vast money and power to finance Karma's deadly mission.

Lee Hyena was the daughter of Lee Myung-jun and a student at Seoul Unro High School. She suffered horrific physical and psychological torment from her classmates. Tragically, the non-stop abuse drove her to commit suicide. Her death is the central event that starts the entire story.

Moon Yejin is the top-student class president at Seoul Unro High School. She maintains a sweet, polite, and perfect reputation in front of teachers and adults. In secret, she was one of the cruelest ringleaders behind the torment of Hyena. She uses her smart front to hide her dark, evil personality.

Song Eunjin is a sadistic bully who terrorizes her fellow students. She relies on her rich background and her dangerous brother to avoid consequences. She takes great pleasure in tormenting vulnerable girls at school. Because of her actions against Hyena, she becomes one of Karma's main targets.

Sehee and Yeeun are Song Eunjin's loyal best friends and constant sidekicks. They follow Eunjin everywhere and eagerly help carry out her abusive commands against vulnerable students. Together, they actively participated in the severe harassment that pushed Lee Hyena over the edge. Both girls rely entirely on Eunjin's social status to intimidate others without fear of consequences.

Chulmin Shin is Moon Yejin's innocent, gold and kind heart boyfriend and an influential student at school. He uses his social standing and status to back Yejin and reinforce her high position. He enables her actions and helps protect their inner circle's authority over the rest of the student body.

Baek Seongchan is Lee Myung-jun's highly capable personal secretary and right-hand man. He acts as the operational manager for the entire revenge plan, providing Yoon Karma with intelligence, resources, and logistical support. Calm and efficient, he handles all the behind-the-scenes work to ensure their mission runs smoothly without drawing unwanted attention.

Sihoo Lee is a popular student at Seoul Unro High School and the object of Song Eunjin's intense crush. Holding high status in the school's social hierarchy, he is admired by many, and Eunjin constantly tries to impress him. His influence among the top students makes him a key figure in Eunjin's social circle and personal motivations.