Nomura says he intended it to be obvious who's heart Terra has connected to, "listen to what Xehanort says, and read the reports". But I've read the reports and watched the video again, and I still don't have a clue.
The only person I can think of is Riku, because he's the darkness to Sora's light, but there really wasn't any indication of that anywhere.
Reason: Riku defeated Roxas with and without a keyblade. Roxas defeated Sora (not counting the little gey keyblade summon that Roxas obviously knew was possible and shouldn't have been surprised about whatsoever). Sora defeated everyone else. Therefore Riku > everyone else.
Hah.. they are in the exact same positions as Sora, Kairi and Riku were... Perhaps this should lead to speculation?
LIKE AXEL BEING RIKU'S NOBODY. dun dun dunnn....
It actually would explain a lot really... Axel's contrasting hair color (I know Nomura said it was from Reno but shh), his tall height, his coolness~, heh even his friendship/fights with Roxas. :P