Speculah:Pillar System Theory
Once upon a time no longer, the "Real World" collapsed. The result was a void in which even "time" and "space" couldn't exist as concepts, and the only only existences that persisted were souls. Some souls were stronger than others; their dreams and desires imposed themselves on the nonsubstance of the void, and became bubbles of newborn "reality." These bubbles were called Labyrinths, and their creators were called Witches.
The Witches could subsume the dreams and desires of lost souls within the void -- drawing them into their Labyrinths and giving them new lives. The Witches' dreams became the dreams of their 'subjects' -- called Familiars. Forcibly uniting the wishes they subsumed, the Witches encouraged the growth of their Labyrinths such that, to their inhabitants, they began to resemble the long-lost "Real World." Soon, the void was filled with Labyrinths, and the souls clung to each other and survived.
Familiars of sufficient independence and braveness would sometimes venture into the void to save more lost souls, establishing their own Labyrinths. Occasionally, Witches and Familiars entered conflict by attempting to subsume the Labyrinth of another, snatching Familiars and claiming them for their own. In the course of these conflicts, a certain entity made himself known. He was called Kyuubey.
Kyuubey possessed the ability to transform normal Familiars and lost souls into 'incomplete existences' -- called Magical Girls to reflect their lack of maturity. Their abilities were "designed" explicitly to subsume the dreams of Witches, collapsing Labyrinths. Being that the Labyrinths they invaded were foreign to them, they could not comprehend the concepts that fabricated local reality. As a result, though the inhabitants and the ruling Witch of a given Labyrinth appeared human to each other, to the Magical Girls, they would appear as strange, psychedelic creatures. Conversely, because the Magical Girls were made of concepts not local to a given Labyrinth, they would appear to inhabitants as incomprehensible monsters, invading 'reality.' Naturally, the Witch and her familiars would defend their world from such invaders.
At some point in the meta-time of the void, prior to "Present Day," a certain Familiar with an immense dream was approached by Kyuubey. What happened after the encounter is unknown, but the Familiar was transfigured into Witch -- the Witch of Witches. Her power subsumed many Labyrinths, uniting them into a near simulacrum of the "Real World" -- a reality in which she was a simple girl named Madoka, unaware of her role as a Witch. Kyuubey was not amused. There were certain limitations to his power, and one of them was that he could not alter somebody who refused to give him permission to tamper with their soul -- he was a being of concepts, and lack of consent was a concept he could not defeat. Employing his mahou shoujo, however, he could engineer a situation to convince this 'Madoka' into lowering her defenses and letting him change her.
If he had his way, the "Real World" would be destroyed once again ...