The story of the Gunparade series takes place in an alternate reality. By the end of World War II, in 1945, an alien race called the Genju suddenly descended upon the war-torn Earth to take it over. Suddenly, the world has a much bigger thing to worry about than simple matters over pride and land. These aliens are out to wipe out the human race!

United for the first time in human history against an unprecedented threat mankind have fought the Genjyu for over half a century, only to see their world slowly swallowed by the devastating foe invading the planet. Jumping forward to present day (sometime in the year 1999) in the Japanese region of Kyushu we discover the humans are fighting back with newly devised weapons known as Humanoid Walking Tanks (HWT), and the hideous power which is the PBE bomb against the Genju "Brains" leading the assaults on the few safe havens that remain.