Echoes Of Fate

Throughout many fairytale stories, it always starts with "Once upon a time...".
But this is no fairytale, so we will start even before time: At the every beginning.
The little tale goes like this:
Many, many eons ago, when the universe breathed its first sign of life, they appeared.
They were the very reflection of each other, being two sides of the same coin; One was the embodiment of hope, peace, order, of the light. Another governed chaos, despair, discord, of the darkness. A perfect balance of scales, never to be tipped to either side, never to interfere.
They remained ever watchful of life and death, no matter where or when, forever.
...
That's how it should have ended as all fairy tales did.
But forever is too dull a word to end a story and as said before, this isn't a fairy tale. Instead, let us tell you what actually happened next:
After an eternity of watching, insanity ripped one apart, fragments falling into the abyss of worlds.
At the realization that the universe will eat itself out to replace the missing half, the remaining half sought to find and rebalance the scales before its too late.

I wonder which ending fits this story best, a reunion or destruction?

[This is a crossover of different anime and manga with my OCs]