Have an omake.
The Infinite War
Once, long ago, there was a great war between Darkness and Light, over the ultimate weapon, the x-blade. They committed their numbers, their strongest weapons, the Keyblade wielders. The battles were cataclysmic, destroying entire worlds. The works of magic in this war were both awe-inspiring and terror-inducing, there were blizzards so powerful that they froze the world, meteors so numerous that they blotted out the skies, fires so hot that it boiled the seas and burned the atmosphere, monsters bigger than mountains were summoned, and it was often difficult to tell which side was which. In the end, the x-blade shattered into the seven shards of light, which made their way into the Princesses of the Heart, and the thirteen shards of darkness, which were lost.
The light was reduced to a fraction, of a fraction, of a fraction, of their former numbers, but they had a few Keyblade wielders left, while the Darkness seemed to have none. The Light came out slightly ahead, but this wasn't the end of the war, only a lull in the fighting. For the Darkness had a powerful weapon, the Heartless. They were beings of darkness that consumed hearts to make more of themselves, and the only way to permanently destroy them was with a Keyblade. At first they swarmed over worlds, with little meaningful resistance to their relentless advance. Unfortunately, they soon learned that the Light was consolidating.
It created the great Champions of Light, more powerful then the greatest heroes and villains of other worlds. It had them gain strength slowly, to think that they were doing it on their own, so that they would build up their willpower. It would "fail" to save others from the Darkness to give them more reason to hate and distrust it. Most importantly, it would fetter them, give them powerful bonds infused with light, connecting their hearts with that of others, so that they would always be pulled out of Darkness, willing or not.
These Champions crushed the every thing the Darkness throw at them. At first, it tried sending hoards of Heartless, but that failed. Then it tried sending its elites, its stronger warriors, but that too failed. Finally, it sent the strongest it had, its largest, its smartest, and its most powerful, but they also failed. The Darkness might have consumed countless worlds, but where ever these Champions walked, the Darkness failed. Perhaps it is time for the Darkness to get its own Champion to fight the Light's, some thing better then Xehanort? Perhaps it is time for a new star to rise in the Darkness, for the dark shards of the x-blade to be found? Perhaps it is time for things to change?