Y/n, a seemingly innocent Japanese transfer student in Seoul, hides a dark secret: she was once the world's top assassin. With the support of her timid younger brother, Jaehyun, she seeks a fresh start in high school, befriending Minho and Minji. However, her past threatens to catch up with her as she encounters Ateez, the city's most feared mafia. Y/n’s unique blue eyes, a known identifier in the underworld, force her to conceal her true identity to protect her new life. Balancing her dual existence, she navigates the challenges of high school while desperately trying to keep her secret safe from those who could expose her.