chaos king was actually the very first oblivion, when the universe cycles through destruction all the abstracts are recreated with the new universe, chaos king was the very first oblivion
the creation event weakened chaos king considerably and when this universe formed the japenese gods discovered him(in a pocket dimension) and named him mikaboshi they then proceded to populate his dimension with gods and forced this severly weekend enitity to the underworld were he had no choice but to plot his way back to position.
after eons of planing he is now on his way to get back his position as the primal void and undo creation
this pretty much sums up everything