Do you know that rock on the other side of Destiny Islands during the second day? The one you need to push into order to get some mushrooms? Well, I like jumping at it from an odd angle to make Sora float in the air. If you do that long enough, the rock will explode.
That's a good point, but it still doesn't explain what Terra meant by "It isn't you that I have chosen." Maybe the reason why he's shown at Destiny Islands is to pick out the successor for the keyblade and thought Riku would best suit it. However, the keyblade still had some will of its own and went along with Sora, as you've said.
I think it was more of Sora getting ready just in case the guy was an aggressor. Though it doesn't seem too much like it to me. ...aside from the appearing out of nowhere bit.
In any case, I think Terra was the one who sent the keyblade to Destiny Islands and he chose Riku to originally wield it. However, this is only a small detail and I'd like to hear theories elaborating on it or other possible connections between Terra and Sora's keyblade.
This has been bugging me a for a while, but I'm not quite good at theories, so I'll just give you what I know for certain.
It's been stated a lot that Riku was supposed to be the wielder of the keyblade instead of Sora in KH1, right? Except Sora received it because Riku temporarily got tempted by darkness and all.
I sort see a connection between that and Terra. In translations of Terra's pre-battle scene in FM+, Terra says something like "It isn't you that I have chosen."
Now, I think Terra's talking about the keyblade but beyond that I don't know. Anybody willing to draw up a better theory? I'd appreciate it.
You know how near the end of Roxas' sixth day, Namine gets dragged into a dark portal by DiZ and after that scene, Roxas gets the item "Namine's sketchbook" or something? I was wondering if someone could give me a nice quality screenshot of that item, since I think the symbol might be important to the story. After all, when Roxas drew it on the table, the heartless and nobody symbol was already drawn.