The narrative is presented from the first-person perspective of protagonist Keiji Kiriya. Keiji is a new recruit in the United Defense Force, engaged in combat against mysterious creatures known as "Mimics" that have besieged Earth. Keiji is killed during his first sortie, but due to an inexplicable phenomenon, he awakens having returned to the day before the battle. He finds himself trapped in a time loop, with his death and resurrection repeating endlessly. As Keiji navigates these time loops in an attempt to alter his fate, his skills as a soldier improve.