An ancient story is being told around a fire; an old man, speaking in a foreign language tells this story grimly. About one giant tribe, who began warring amongst themselves:
One side believed that the others had begun sinking into a darkness, beginning to call them the "Tainted." The separated ones began calling themselves the Cetra, and fought hard to keep the old ways. But the Tainted had already begun using the land to form the Tainted Weapons.
Afraid of what these dark planet-made creatures could do to themselves and the land around them, the Cetra fled, via portals to Gaia, a brand new planet they could call their own.
Still fearing the Tainted would follow them and try to wipe them out, the Cetra used Gaia to form their own Weapons, guardians of the Planet they had begun to call home.
Due to unfortunate events concerning a Sephiroth Essence and Jenova, these Weapons are no longer available to protect Gaia from the Tainted.
Now, the Tainted and their dark Weapons, after having depleted their own resources in their world, have begun the transfer, wanting to take Gaia as their own...