Shock Horror!
Alot of characters from prevous Final Fantasy have had some big thing revealed about them like:
Cecil: (SPOILER)Moon Man (I think)
Terra: (SPOILER)Esper (That count?)
Cloud: (SPOILER)Had the thoughts of someone else
Squall: (SPOILER)This one isn't so big I guess, Laguna's his dad and he grew up with all of his party members. except Rinoa.
Zidane: (SPOILER)Comes from another planet
Tidus: (SPOILER)Dream of the Fayth
There could be more, but anyway suggest what you think Vaan is going to be.
Edit by D: Spoiler tags r0x0r, j0.