So I did pay attention to XIII's plot even if it didn't interest me. Bart wanted to kill everyone on Cocoon to summon the Maker who created humans and fal'Cie. This is told to us repeatedly.
It's all bunk. There is no Maker/God, humans and fal'Cie wee made by two completely separate entities who themselves are fal'Cie and basically it renders everything the main villain expositioned to us worthless. It's all so unnecessary and stupid.