On the Sentai Mountain, humans work side-by-side with intelligent robots in mines. They use large excavation machines to dig out, gather, and transport mined rock to the surface. Unfortunately, an error occurred in one of the machines, and it sparked a vicious rebellion. Robots turned on their human masters, and through the fighting a series of mysterious explosions blasted the mountain into two halves. The robots were eventually driven deep into the newly-formed canyon far below.

Peace was restored, and the humans began building long bridges to span the two halves of the tall mountain. But deep underground, the robots came together again, and grew quietly; rebuilding their mining machines into powerful Battle Machines with armor and weapons. Their surprise return ignited another furious war, which allowed them to take control of half of Sentai Mountain. The robots were about to take on the second half when they were halted by a secret human project: Exo-Force. The humans had quickly assembled a team of warriors, and built their own Battle Machines to counter the robots.