The planet is facing an invasion from strange creatures known as "Mimics," sparking a worldwide war where humanity must fight to survive. The United Defense Force is created to combat this menace, with the sole aim of eradicating the Mimics. Combat suits with exoskeletons are distributed to soldiers to enhance their abilities against the ever-present danger.
Keiji Kiriya, a fresh recruit, unfortunately meets his end on his first mission. In a surprising turn of events, he wakes up the day before the operation. Keiji soon realizes that he's caught in a time loop, reliving the same day repeatedly. With each repetition, Keiji hones his abilities and strength, determined to use his experience to alter his future and face death with bravery.