I just bought Kingdom Hearts the yesterday and so far I love the game (Especially like how you can duel Wakka at the beginning and slap his blitz balls right back at his head!) but I got a question, which might be answered later in the game but I am impatient (and this is one heck of a run on sentence!

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Does the game ever explain how Final Fantasy characters like Wakka and Selphie (FF X & FF 8 I believe) are on the same island together when they are from seperate worlds & possibly seperate times? Or how Tidus is even there since he was nothing more then...Well, I don't want to give a spoiler for X so I will just say he never grew up with Wakka. And how is Cid (From FF 7) is on Traverse Town.
I know it sounds nit picky, but I like to know if there is an answer to these loose ends.