High school student Aoba Watase is suddenly attacked by a giant robot called a "Valiancer," but is rescued by his enigmatic classmate Hina Yumihara. Hina reveals herself and the robotic enemy to be from the future, propelling Aoba forward 70 years to save his life. Arriving in the future, Aoba finds himself in the cockpit of a Valiancer named "Luxon," thrust into a battle between the Free Pact Alliance (FPA) and the Zogilia Republic. After successfully coupling with FPA pilot Dio Weinberg, Aoba's skills rapidly improve. But his reprieve is short-lived as the FPA ship Cygnus takes him into custody, intending to interrogate him. Not knowing whether he will ever return home, Aoba is about to discover he is caught in a war to protect the world.