That rule that differently numbered Final Fantasy games exist as entirely separate entities rather than direct sequels? Not exactly a hard and fast system. You see Final Fantasy X and Final Fantasy X-2 are very, very distant prequels to Final Fantasy VII. The evidence? Final Fantasy X-2’s Shinra.
Shinra is a technical boy-genius, and the creator of the game’s Garment Grid system, But he had a much greater scientific ambition. Recognising the Farplane (Final Fantasy X’s afterlife) as a potential source of limitless energy, he aimed to eventually harness it in order to power the planet. Given that the Shin-Ra Company in Final Fantasy VII had exactly the same plan, wishing to draw Mako energy from the Lifestream, doesn’t all of this smack of a little more than coincidence?
Series writer Kazushige Nojima has even admitted the connection, stating of Shinra in the Final Fantasy X-2 Ultimania retrospective book,
“…he is unable to complete the system for utilising this energy in his generation, and in the future, when travelling 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.”