Well, I'm already stumped, because I don't really remember the names of the keyblades in the game. I think the answer is Dreamweaver but I don't remember if the Olympus keyblade is actually called Olympia.

On the other hand, I cannot think of which world the Dreamweaver keyblade would come from. It sounds like it would come from the Sleeping Beauty world but that does not appear until KH: BBS.

In the end, I cannot risk it. So I will take a 50:50 lifeline.