I understand your point, but I still don't think Vanitas' situation is comparable here.
The thing is, Vanitas looks like Sora. I think this shows that Vanitas shares Ventus' connection to Sora, and he gets the same 'filling the empty spaces in my heart' thing. Which means Vanitas isn't really wielding on a cut off fraction of a heart alone.
But, Vanitas wasn't comatose when he was born. And that's prior to when Sora filled in Ven's heart. You could suggest that Vanitas is incapable of wielding (since we never see him do so during this time), but I somehow doubt that, especially when he's already capable of being conscious on his own.
I think that Roxas was able to experience ghost emotions as a side effect of having Ven's heart inside him, but he wasn't connected to that heart. If he was connected, then he should have been getting memories from it as well as from Sora, shouldn't he? But he didn't. Roxas didn't see as many Sora memories as Xion did, but he still had a fair few, if you count every time the bottom screen of the DS changed to show Sora. However, there was no hint that he was seeing memories of Ven at all that I could see. Xigbar saw Xion as Ven, but I thought that had to do with Xigbar's own memories projecting rather than the memories inside Roxas or Xion.
They were Sora's memories flowing into him that got the ball rolling, bringing him out of the blank slate mode. I think that perhaps some of those memories resonated with Ven's heart, and produced ghost emotions, but I don't think there's enough evidence to prove that the Keyblade itself belonged to Ven.
This issue goes both ways, though.
If you ask why Roxas wouldn't be capable of experiencing Ven's memories if he were using Ven's heart throughout Days, you also have to wonder why he wouldn't experience them if he "awoke" Ven's heart at the end of Days, either. We're both claiming that Ven's heart is active at one point or another, without any perceivable memories.
It may have to do with the memories being buried deep in his heart. As Namine says in coded, they were buried deep in Sora's heart, so they may have been buried deep in Ven's to start. It makes sense, considering he's been sleeping for a good decade. In "sleep," as in being taken by the Heartless, I imagine that you gradually forget.
It just makes sense that the Keyblade is Sora's. If it wasn't, then why would Xion become unable to use one when Roxas swings the power balance? lame plot device to force them to spend time together? Noooo
Xion's power hinges on the absorption of memories through Roxas, Roxas' power does not. He had it from the getgo and while he himself got weaker, he never lost the ability to wield. So I don't think Xion's ability to wield really has any correlation to whether or not the keyblade Roxas uses is Sora's or Ven's.
Actually, I was talking about this line
As in, 'from the time that the two were both using the Keyblade at the same time' is referencing what was said previously about them both using the Keyblade, and 'the Organisation itself was using Sora' references Castle Oblivion.
Ah, got ya.
Lol, I'd say the convulsion went into overdrive with Ansem/DiZ/Rikunort/Terranort/Xehanort/what-the-fuck-ever-nort, but at least they explain that in-game....
Right, confusing, but it's there. And the parts that aren't explicitly explained are things that don't need to be. For example, how much of Xemnas was Terra and things of that nature offer some healthy speculation. Even then, though, we're supposed to be getting some hints about that in the next game (presumably 3D).
You'd figuring working out all of this keyblade stuff would be more important, but even more of it is left to interviews.
You know, there was another interview (that Days-era fan powered one) that had paraphrased him as saying
and him saying 'Sora's power' made me think that the second blade is Sora's, back when I first read that text (another translator did it on Heartstation, I can't remember how they actually translated the line).
So, in conclusion, who the fuck knows. I guess we just have to wait and see if we're tossed any more bones.
Just shoot me.