Creatures of Shadow
Once upon a time, the ancient shadow-dwelling race known as the Umbrum performed an act of life-giving mercy for the struggling tribe that would one day be known as the crystal ponies. When the crystal ponies recovered and opted not to repay the Umbrum for their kindness, the insult swiftly lead to unrest and animosity. Violence and destruction erupted in the lands of the Frozen North, but the beginning of strife's end arrived when Sombra, king of the Umbrum, lost his heart to a compassionate healer named Radiant Hope. The affection was mutual, and as the gentle crystal pony agreed to join Sombra in his realm, the hostilities softened. It seemed, at last, that love would conquer all.
But lasting peace would have a price, and the Umbrum still demanded tribute from the offending tribe. That payment would come in the form of sacrifices; Hope loved children, and as she could have none with her ethereal husband, the crystal ponies were required to periodically give up one of their own. But even here could be found a boon. The royal couple were more than happy to accept the terminally ill…as sickness does not exist in the realm of Umbra, the little ones would become whole and well under Hope and Sombra's loving care. The truce, and the agreement that accompanies the promise of peace, still persists to this day.