The Red Stone was a fragment from a larger Meteor. Unlike all other fragments of that original meteor, the Red Stone is unique. The energy within the stone would not diminish like all other fragments. It's power output was practically infinite. After acquiring it, Exaton incorporated the stone into his armor.
While the stone made Exaton virtually invincible, it also caused him great pain. It even caused him to feel immense rage, leading him to attack his own followers.
Working together, the Golden and Dark armies were able to subdue Exaton long enough for Leo to get close enough to remove the stone from Exaton's armor. Once removed, Leo flew the stone high into the air and destroyed it.