Equestria was once ruled by what we know as Celestia and Luna. But, they were not always kind and merciful. They once were tyrannical beings of absolute power. That was their primal being. Since then, they have contained their power and become civilized. However, when the two sisters lose control of their primeval powers, when their alternate forms take over, there is no assurance of safety.

Cover art: "It's Too Late..." by The0ne-u-lost
deviantART page: http://the0ne-u-lost.deviantart.com/