Kingdom Hearts Episode 18: End of the World

"End of the World is a by-product of all Heartless' destructive nature. Although End of the World is the last world, the Heartless are not very numerous as compared to Hollow Bastion, but they are very powerful. Upon taking a world's heart, a tiny fragment of what is left of that world is sent drifting through the void of space until it eventually meets and merges with End of the World."