The Worlds of Final Fantasy, Conected or not and if so, how?

[RomildaRayne]

All speculation, and, as source materials such as the Ultimania guides and interviews with SE's past and present FF development team members such as Hironobu Sakaguchi have proven beyond all doubt, each FF world is independent of the other - they each take place in their own separate universe (or, in FFV's case, three universes!).

Except that FFVII and FFX share a universe; the Al Bhed named Shinra's descendents eventually leave Spira and use the technology he was developing for use on the Farplanes to create the Mako Reactors and harness the Lifestream. This is stated in Final Fantasy VII Ultimania Omega and Final Fantasy X-2 Ultimania.

The Depths of the True Moon in Final Fantasy IV: The After Years, which unlike the optional dungeon in Final Fantasy IV's re-releases cannot be considered non-canon, is also a veritable boss rush of enemies from Final Fantasy I to Final Fantasy VI summoned by the Creator.

To be clear, I don't agree with the above speculation, but the Final Fantasy Universes are connected to an extent.

[WellFooled]

Except that FFVII and FFX share a universe; the Al Bhed named Shinra's descendents eventually leave Spira and use the technology he was developing for use on the Farplanes to create the Mako Reactors and harness the Lifestream. This is stated in Final Fantasy VII Ultimania Omega and Final Fantasy X-2 Ultimania.

Kazushige Nojima said this in that Ultimania:

After quitting the Gullwings, Shinra received enormous financial support from Rin, and began trying to use Vegnagun to siphon Mako Energy from the Farplane. But, he is unable to complete the system for utilizing this energy in his generation, and in the future, when traveling to distant planets becomes possible, the Shin-Ra Company is founded on another world, or something like that....... That would happen about 1000 years after this story, I think.

The words "or something like that" and "I think" suggest to me that these are just his musings, nothing set in stone. Its very likely these ideas were what produced the character of Shinra in FFX-2, but they aren't included in the game. If every musing from the developers were canon, Tidus would be a construction worker and Cloud would have slicked back black hair.

FFVII's Ultimania just asks a question:

The results of this cannot be seen in FFX-2, but maybe one day his descendants will establish a "company that supplies the energy of the planet"?

Again, it flirts with the idea, but never confirms it and none of this was ever stated in either of the two games.

To be clear, I don't agree with the above speculation, but the Final Fantasy Universes are connected to an extent.

They're all connected in the fact that in the real world they are all part of the same game series so naturally there will be reoccurring things that can't be explained in lore, but sometimes it doesn't need to be. Bosses from other Final Fantasy games show up in bonus dungeons because it's a video game, it isnt explained in the canon of the game's universes because they don't need a reason beyond that.

[RomildaRayne]

They're all connected in the fact that in the real world they are all part of the same game series :p so naturally there will be reoccurring things that can't be explained in lore, but sometimes it doesn't need to be. Bosses from other Final Fantasy games show up in bonus dungeons because it's a video game, it isnt explained in the canon of the game's universes because they don't need a reason beyond that.

I agree with what you've said until this point because the (True Moon's) Depths are not an optional dungeon; I specifically made the distinction between the bonus dungeons in re-releases of Final Fantasy and Final Fantasy IV for that reason. There is a purpose, in the lore, for those bosses to be there as they were summoned by the Creator, even if it is mostly fanservice. Gilgamesh actually calls out Bartz's name, making it almost certain that he is the same Gilgamesh of Final Fantasy V.