the truth is here!
I think Mystgun is Edoras' Gérard and his story is something like:
When he was a child he was hold as a slave with some friends and met Erza (edoras one) but she became mad and turned her back agaisnt him and casted him out of Edoras to Earthland.
Following the basis seen so far with every character counterpart of Edoras I find this prediction to be very likely or at least something along those lines.
Also, i heard a rumor that in Edoras you could only use magic with magical objects like the staff natsu is holding the cover of the latest volume or something. not sure if its true, but mystgunner is always carrying staffs on him so that may help
Well, now that Mistgun's history is more or less cleared up and everybody knows that Gerard and Mistgun aren't the same person at all, I thought about some other stuff, mainly about Gerard.
Let's face it, as he's basically a recycled Sieg Hart from Rave (hell he even got recycled two times because he's just that awesome :P) don't you think he just HAS to play a rather large role in the later parts of the story?
Sieg defeated a pretty much invincible opponent at that time (Haja), was the Guardian of Resha's grave and on top of that he was responsible for all the reinforcements arriving at the scene of the final battle, after all.
So I predict that Mashima has something similar in mind for Gerard. Someone like Urtear comes to mind as a fitting opponent for such a battle, as she was the one responsible for his earlier downfall, with him leading the council into firing Aetherion and trying to resurrect Zeref and all. And having him showing up as an ally to Fairy Tail in a showdown against Grimoire Heart would be just awesome. :>