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Satan was the one that created their alliance and also the one that presented them the Usurpers of Destiny, a Multi-Dimensional Level Faction that spanned through thousands of different Universes. They had many goals; however their primary goal was the gathering of the Origin World Fragments and the assimilation of all Universes, most of the time by force.
Even now, they were still mysterious, and these goals were the most surface level things they had guessed. Satan received an invitation from the Outer Gods long ago, and decided to join without hesitation, desiring power above all things.
After all, the Usurpers of Destiny's true plan was to overtake this Universe as well, which most said was a Universe with a ridiculously high quantity of Origin World Fragments. The biggest amount they have ever seen across hundreds of Dimensions.