Sephiroth as he is now wouldn't really work as Aerith's lover. Gotta rework the story line a bit. I've thought of this pairing before and I really dug the idea of Sephiroth escaping the Reactor and going to look for the last surviving Ancient, since he's kinda hopped up on the idea he's one of them now. I've never really thought of it beyond that bu I think it could work.

Anyway, FFVIII with Seifer as the Hero, as it was intended to be.

FFX, it turns out ALL of Spira is a Dream as the War 1000 Years Ago killed pretty much everyone except for a few Summoners who conjured back all the races and people they had known in a desperate attempt to avoid absolute extinction. By killing Sin you end all a\sapient life on the planet.