Ten years ago, the scientist Cathabel transformed children into Gunners. They were tasked with fighting the Knivers—criminals who became blade-like humans through the “miracle” of Raito. Chiara, a young soldier, is assigned to capture Gun, a Gunner believed to be involved in the massacre of Cathabel and the destruction of the “Gunner” project.

However, behind her assignment, Chiara has her own plan: to avenge her father, one of the victims of the massacre. Chiara hires a Kniver to kill Gun. But unexpectedly, the hired Kniver acts beyond Chiara’s control, forcing Gun and Chiara to face the Kniver alone. Eventually, the true events of the past are revealed.