Enforcer Teppei Sugou, previously the top pilot in the National Defence Army's 15th Integrated Task Force, is approached by a scout from the Ministry of Foreign Affairs who proposes that he rejoin the military. While pondering the proposition, Sugou remembers his final months of service. During his last mission, named Operation Foot Stamp, his team launched a top-secret military assault on the Southeast Asian Union. The mission encountered significant issues, resulting in Sugou's First Guardian drone being instructed to provide air support by dropping emergency supplies before returning to base. Despite Sugou's personal reservations, he obeyed the orders and left his comrades on the ground. Numerous casualties occurred during the operation, including that of Sugou's commanding officer, Itsuki Ootomo. However, three months later, Otomo was identified in security camera footage of a massacre at the Ministry of Defence, leading to him being labeled as a suspect in a terrorist attack. Sugou collaborates with Enforcer Tomomi Masaoka and Division 01 of the Criminal Investigation Department as they track down his former mentor.