Well, considering that Bahamut's Triple Triad Card is darkness element and that the attack he used that was considered a calamity although it did not span the entire world, was considered non elemental.
Some think that non-elemental is just the combination og all elements.

I think there still are 6 reflections including the Thirteenth. So I think the story will seek out to purify the Thirteenth of its darkness similar to how we purified the first of its light.