In the original game, they very much implied that there was just one key (Riku "made" the one he used in that game and Mickey's keyblade at the end was meant to be a surprise).
But then, for KH2, they decided "**** it, let's give EVERYONE a keyblade!"
So now Riku has one. And we don't know how he got it. Nor why it looks exactly like his Soul Eater (the bat wing-shaped thingy). Did it transform? Did he just glue a keychain to the hilt? Did he finally get enough tickets at Chuckie E. Cheese to buy it? No one knows.
And Kairi had one for, like, a minute. And no one knows how she was able to use it or where it came from or why it needed so many god ****ed flowers on it. And it was never elaborated on at all for the rest of KH2. Totally superfluous scene that did nothing but further hinder what was already shaping up to be a cluster **** of an ending.
Good god, plot holes big enough to drive a Hummer through in that game.
Sorry for the rant, but the "everyone gets a keyblade and we're not even going to explain why" thing has always bothered me. I'd hope for BbS to clear some things up, but I'm sure it won't.
*cough*
>_>
Sora for Brawl