As a huge fan of Final Fantasy, I always believed that the games are linked by the fact that they are a multiverse: a series of dimensions linked together in some way. And there is evidence to this, as you’ll see here.
Crystals seem to be the foundation of life in the series, one way or the other.
Characters appear in different worlds…
The same species of creatures show up time and time again.
At least one Cid exists in all the worlds.
And of course, all of the Final Fantasy heroes and villains had their big super cross over in Final Fantasy Dissidia!