Killer Girl K(2011)

Killer Girl K is a South Korean thriller series following Cha Yeon Jin, a high school student hiding a deadly secret. By day she appears like any other teenager; by night, she's a skilled assassin driven by a single purpose: avenging her mother's murder, which she witnessed firsthand. To get close to those responsible, Yeon Jin infiltrates SS1, the shadowy organization connected to her mother's death, by joining their ranks as a killer. As she navigates the dangerous world of contract assassinations and organizational politics, she hunts for the person who destroyed her family while maintaining her carefully constructed cover at school. The series balances intense action sequences with the psychological toll of living a double life, exploring themes of vengeance, identity, and the cost of obsession.