I've got a whole new idea. FFVII and FFX r the best final fantasy games and an excellent sequel to ffx-2 would be a prequel to ffvii.Shinra mentions something about extracting energy from the planet and thats wat Shira corp. does in ffvii. the pyreflies could be that source of energy. In ffx2 the farplane is underground and it could mean that the farplane reaches deeper into the planet till the planet core where would be the most pyreflies. An alien invation could come to use those pyreflies from the planet core as energy.Since the fayth r not really dead it could explain how the summons in ffvii and the eaons in ffx are very similar.Also the mateia in ffvii is kinda other kind of the spheres used in ffx.In FFVII:advent children Sephiroth mentions something about leaving the planet in a ship if the planet dies, so it could mean that the they ( their ancestors) got there from other planet.

Spira could have been renamed to (whatever the planet is named in ffvii).

Alien dont necessarily need to look like monsters so the ppl in ffvii could the mixed races of the aliens and the spirian ppl.



PS:i've not played FFVII so i may be wrong.