In 2112 Teppei Sugou is a drone pilot with the Defence Army's 15th Integrated Task Force, flying overwatch for a ground squad in Okinawa under the callsign First Guardian, when the operation goes wrong and the unit led by his commander Itsuki Ootomo is written off. Three months later an unmanned gunship opens fire on the Ministry of Defence in Tokyo, and the drones are traced back to Sugou's own military terminal. Inspector Risa Aoyanagi and Enforcer Tomomi Masaoka arrive at his base to work out what really happened.