Although cheerful and delicate, Sakura Sakurakouji is a skilled martial artist with a steadfast sense of fairness, regardless of the situation. While riding a bus home, she witnesses people burning in blue flames. She calls the police to bring the murderer to justice, only to find that no evidence remains. However, all her doubts about what she saw vanish the next day when the new transfer student, Rei Oogami, joins her class; he is the very boy she watched commit murder in cold blood. Rei is kind, sweet, and quickly becomes popular, which contradicts Sakura's accusations. Soon enough, she learns his true nature: a Code Breaker, or "one who does not exist." To Sakura's shock, Rei, armed with mysterious powers, seeks to exact justice according to the principle of "an eye for an eye." Determined to bring Rei to the right path, Sakura keeps close to him in the hopes of redeeming him from his ways before others are hurt.