'GEAR System' - The system revealed by Atsuga Corporation in the mid-21st century revolutionized all technologies, allowing for the perfection of piloted humanoid robots called 'GEARs'. During World War IV in 2050, GEARs from all over the world went berserk and began massacring humanity. The berserk GEARs, known as 'RAGE', conquered the surface world and pushed humanity to the brink of extinction. The remaining survivors escaped underground and began their counterattack. After over 50 years of w...