The year is 2047 when the Earth is suddenly attacked and destroyed by an unknown alien life-form, wiping out all major cities in one swift blow. In an effort to stop the invasion codenamed FOS, the survivors come together to construct a Diffusor and achieve a temporary peace. Fast forward to the present in 2053, where the final counterattack to take back the Earth - Plan Zed - is put into action. Hiroshi Akishima, an alliance soldier in the Planetary Defense Forces, seeks vengeance for his father's death at the hands of the aliens six years prior. However, the Diffusor must be dropped for the offensive, leaving humanity unprotected once again. The question remains whether or not mankind will prevail and win back their planet, or if their ultimate and final gamble will end in defeat.