Now, I'm well aware that there isn't ever going to be another FFX-related game. The Rikku/Yuna-starring X-3 idea was abandoned long ago; there was some consideration given to an Auron/Braska/Jecht prequel, but that story - and its conclusion - are told in FFX, so that idea died quickly, too.
However, there's another prequel possibility that occurred to me.
I don't know if it's been suggested before; if it has, I've never seen it.
But there's one big bit of back-story to FFX's characters we're never shown in full, one that'd make an interesting game, I think:
Lulu.
Think about it... she was a fascinating character in FFX; multi-faceted and mysterious. We know a little about her history, just enough that it'd be a great game without having been utterly spoiled already.
We don't know exactly where Lulu's from; she's definitely not a native to Besaid, but we don't know how she got there after her parents' deaths.
We know she was once involved with Chappu, Wakka's younger brother. It'd be good to see their interactions, and how she reacted to his final 'career move'. Then there were the two pilgrimages she went on, one ended by her summoner's death on Gagazet - potential for some riveting new characters there - and the other which failed when her summoner lost his nerve, in the Calm Lands. This'd provide a whole different look at summoners' lives and roles in Spira, as well as the personal struggles of the guardians. It'd be good to see Lulu's changes; when she became a 'dark' and broody sort, what she was like before, that kind of thing. I believe she lost her left eye at some point; she's definitely fought a lot of battles, so a new game would be a good way to learn about what she really went through up until the beginning of FFX.
That, and it'd be another chance to hear Paula Tiso's perfect voice-acting, too. She conveys Lulu's intelligence and wit so well.
