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 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.
These 'creators' could subsume the dreams and desires of lost souls within the void -- drawing them into their Labyrinths and giving them new lives. Their 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 its inhabitants, it would begin to resemble the long-destroyed "Real World." Soon, the void was filled with Labyrinths, and the souls that had lost their way clung to each other and survived.
Familiars of sufficient independence and courage would venture into the void to save more lost souls, establishing their own Labyrinths. As they were unable foreign Labyrinths as coherent space, Witches and Familiars occasionally entered conflict by attempting to subsume the reality of another, snatching Familiars and claiming them for their own. In the course of these skirmishes, a certain entity made himself known. His name was Kyubey.
Kyubey 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 and absorbing wishes until they themselves could mature and establish their own Labyrinths. Being that the Labyrinths they invaded were foreign to them, they could not comprehend the concepts that fabricated the local reality. As such, though the inhabitants and the ruling Witch of a given Labyrinth would appear human to each other, to Magical Girls, they looked like strange, psychedelic creatures. Conversely, because Magical Girls were made of concepts not local to a given Labyrinth, the girls appeared to Familiars and Witches as incomprehensible monsters, invading 'reality.' Naturally, the Witch and her Familiars would defend their world. Simply observing, Kyubey took glee in the progression of his plans.
At some point in the meta-time of the void, prior to "Present Day," a certain Familiar with an immense dream potential was approached by Kyubey. What happened following the encounter is unknown, but the Familiar was transfigured into a Witch -- the Witch of Witches; the Grand Goddess. 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 true role. Kyubey was not amused. If he had his way, the "Real World" would soon be destroyed once again ...
There were certain limitations to Kyubey's power, and one of them was an inability 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 magical girls, however, he could engineer a situation to convince the overly naive 'Madoka' into lowering her defenses and letting him change her. Her dream, unsupported by her power, would end, and the souls of her Familiars would be lost again to the void.
However, there was an Irregular in the system -- a magical girl Kyubey created long ago, who defied his manipulations. She knew of his true intent, and she would stop at nothing to prevent Madoka from falling into Kyubey's trap. Her name: Homura.