The Black Materia

[Rostum]

I personally liked the Jenova theory, that it originated with her, but looking at the mural in the Temple of Ancients, it does look like this was used by the Cetra before Jenova, hell its possible that Jenova arrived on the Planet while riding the original Meteor spell. So it's possible that its the Cetra's own fault Jenova came to Gaia.

Maybe SE need to milk it more and create another prequel during the Cetra's reign on Gaia.