Rising tensions between the Osean Federation and the Kingdom of Erusea culminate when Erusea launches a surprise attack using a massive number of combat drones against Osean military targets and captures much of the Usean continent, including the International Space Elevator (ISEV). Two gigantic Erusean airborne drone carriers, known as Arsenal Birds, protect the ISEV. During a mission to extract former Osean president Vincent Harling from the ISEV, a missile hits Harling’s aircraft, killing him. Osean pilot Trigger is accused of firing the missile, found guilty by court martial, and is transferred to 444th Fighter Squadron “Spare”, a penal military unit for which Avril also works. Considered “expendable” by the warden, they are sent on several dangerous missions. Trigger crosses paths with Erusean ace Mihaly A. Shilage, who provides flight data to the Erusean drone program headed by the Belkan scientist Dr. Schroeder.