It has been found that there are 4 crystals of power spread throughout the world. Three keyblade masters, one of Light, one of Nothingness, and one of Darkness, have learned this through a page of a book that was mysteriously... there... by each of them in their home worlds.
The page that the master of Light had said that the 4 crystals would bring light and happiness to everyone of every world, also leaving the keyblade master of Light to rule over all the worlds.
The page that the master of Darkness had said that the 4 crystals would bring darkness to all worlds and would allow him/her to manipulate everything, becoming the ultimate ruler.
The page that the master of Nothingness had said that light and darkness would be perfectly equal throughout all worlds, and that the master of Nothing would be able to rule all of the worlds.
Who wrote the pages?
Though each keyblade master received different pages, their goals became the same: Find the 4 crystals.
But what really happens if they do?
Each master is collecting keyblade wielders to destroy others in their way and try to find the 4 crystals.
In the meantime, heartless, nobodies, and unversed are increasing dramatically in population, which only makes everything harder for the keyblade wielders.