Act 1: Age of oneness
In it, a "soul" appeared, capable of creation. A soul, in this context, can only be the opposite of the stagnation that is the infinite nothingness. Those two opposites are: To be active and to be limited. In order to be alive, it has to act - to create. It created time and space, but both also had to be limited in order to be existant. Else it would not be different from the nothingness surrounding it and thus be nonexistant.
Act 2: Age of incation
As space was limited, soon the space was filled with creation. It could be expanded, but the speed in which it could expand was limited, too. Quickly, the universe was full and inaction became its curse, as new creation was only possible at its borders, which was the only place where stagnation did not strike the world.
Act 3: Age of duality
In order to solve this problem, the soul split up in order to create a force equal to it, but capable of a different kind of creation. Each others creation meant the destruction of the others - thus both could create as much as they wanted, for the creation of the one soul meant the potential for creation for the other.
Some call those two forces "order" and "chaos".
Act 4: Age of attachment
The only possible problem with this system was if something was destroyed the other force would not want to be destroyed. In each others interest, the forces agreed not to destroy what the other force would like not to be destroyed. Thus, some realms of the universe stayed untouched by the force opposite to the creator. The rest were "free".
Because of this, four realms existed: The realm of order, the realm of chaos, the realm of freedom and - of course - the realm outside of the universe, the realm of the nothingness.
Act 5: The options
After a while, as hell and heaven grew for more and more creation fell under the protection of the forces, both forces realized that at some point, they would run out of space for creation.
They had thw following options:
A) Enter another age of inaction eventually, forced to repeat the process - since the only way out of it was another split of each forces. Each time a split would happen, as the realms in which they happen it cannot touch each other, they would only have half the space to work with, eventually leading to a space so small that it cannot be split.
Option A is not a long term solution and was thus not chosen.
B) Agree that a certain area always had to stay free and if you create in there, you had to give up some of your already existant creation. But this would mean that all you grow attached to had to be destroyed eventually, defeating the purpose of attachment in the first place. Plus their creations could no longer be equal to each other, their value defined by when they have to be given up. It would, however, solve the problem of stagnation.
c) Make it possible again for each force to affect the other, basically lifting the agreement that protected attachment in the first place. However, since creation speed on both sides was still limited and equal, while there would be conflict it would still mean that each force had their own realm. The realm of freedom would technically be gone (and, at the same time, be everywhere) but stagnation would be gone, too.
Act 6: The choice
"A" was out of the picture right away, so it was a choice between "B" and "C". B was favored by the force of "order", C by the force of "chaos". The solution was, again, another split: Two halves of the universe, both with equal forces of both sides, one takes option B and one takes option C so that there are two universes.
Universe 1 would not allow conflict, both forces would simply give up and create anew. This would lead to a constant "improvement" of both forces realms.
Universe 2 allowes conflict, both forces would constantly "attack" each others territory with their own creation, meaning the others destruction.
Act 7: The unwritten rule of universe 2
Both forces in universe 2 had to constantly make sure that they would not lose an inch of the territory of the edge of the universe, where it expanded and gave both forces new free territory to create in. This expansion was basically the only ressource for creation of each side that didn't have to be taken by force.
Act 9: The stagnation of universe 1
Eventually, after a long time, both realms of universe 1 had reached a state of "perfection" where they simply recreated what was destroyed on each side, as what they had was already "as good as they could possibly imagine". Thus a state of recreated stagnation was reached and universe 1 failed at its purpose.
Act 10: The new purpose of universe 1
To solve this problem, universe 1 required a new reason to create new things. Since universe 2 always had this reason in form of its evolving conflict, the solution was to simply give that purpose to universe 1, too. Universe 1 would reintegrate its versions of "heaven" and "hell" to the realms of their own forces in universe 2, where they could create for the sake of conflict without being attackable.
Those realms would become the unattackable areas for each force, even if completely surrounded they could still send their creation into the world. The free realm of universe 1, now also integrated in universe 2, stayed also "unattackable" and was only meant as potential for creation for both the "universe 1-forces".
Act 12: The choice of repetiton
At this point, only two things can be done in order to avoid this stagnation:
A) Split up the winners realm (which is now in the same dilemma as the original soul in Act 2) and give each half one of the cores.
The following act of choice A would be the same as the end of Act 10.
B) The winner gives up its territory - afterwards, both forces can start from scratch.
The following act of choice B would be the same as the end of Act 3.
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C) Of course allowing stagnation (and thus the death of the universe) at this (or, theorerically, any other) point of the story is also an option. As the energy of the soul in itself is limited, as the universe expands eventually it will run out anyway. Existance, by definition, cannot be infinite. (It can, however, start over.)
The following act of choice C would be the same as the end of Act 0.