Sosei Takarai has a secret: he is a high school student by day and a professional assassin by night. His ability to instantly resurrect each time he dies makes him exceptionally suited for this violent line of work, a family trade overseen by his older sister. What Sosei truly desires is a normal life, and his wish appears to come true when Asumi Shiramori, the most popular and beautiful girl in his class, confesses her feelings and becomes his girlfriend. However, his happiness is short-lived as his assassination job consumes all his time, leaving him unable to go on dates or maintain a typical relationship.

The precarious balance of his double life shatters when he spots Kuchina Hitsujimoto, an aloof and eccentric classmate, at one of his murder sites. Sosei soon discovers that Kuchina is no ordinary student; she is also an agent in the shadowy underworld, possessing a deadly power that allows her to kill any living thing with a single touch. As Sosei is tasked with investigating Kuchina, their fates become intertwined in a dark romance complicated by violence and supernatural abilities. The world itself is built on the existence of "cheats," special inborn abilities that set people like Sosei and Kuchina apart from ordinary society.

As the story progresses, the love triangle deepens. While Sosei tries to navigate his feelings for the innocent Asumi, he finds himself drawn to Kuchina, whose powers eerily complement his own. After Kuchina saves him, Sosei attempts to thank her, leading to an exchange diary that pulls in Asumi and other classmates, forcing Kuchina to confront emotions she was conditioned to suppress by the sinister All-Japan Assassin Association. The narrative explores how Sosei gains lives by taking them and how Kuchina erases life effortlessly, creating a bitter and heart-wrenching quest for a normalcy that remains perpetually out of reach.