Kingdom Hearts Theories and Speculations
I love to speculate on games I know well, and KH is a game (series) I know very well. So here are some theories I've either come up with or heard somewhere else and support, along with evidence as to why I think these things are true.
WARNING: Unmarked spoilers below. Read at your own risk.
1. Cloud is a Heartless and Sephiroth is his Nobody.
There are a few things that point towards this being true. Firstly, recall a line Cloud says to Sora after their battle in the first game. "I fell into darkness, and I couldn't find the light." Then remember what Sora said when he became a Heartless in the first game. "Falling... falling... into darkness". He also later mentions that he saw a "light" (which was Kairi) which saved him from becoming a Heartless for real. Cloud also seems to be mainly driven by emotions, particularly anger - the Heartless are literally hearts that were consumed by darkness, and hearts are the centre of emotion, meaning that most Heartless are driven by emotions. On the other hand, Nobodies are unable to feel emotions at all, and therefore are mostly cold, calculating and cool - which is exactly what Sephiroth is like. Sephiroth also mentions being Cloud's "darkness".
2. The Gullwings appear as fairies because they had a spell cast on them by Maleficent.
Self-explanatory, really. Perhaps Maleficent thought as fairies they'd be less likely to try and rebel against her.
3. Kingdom Hearts III will feature both Master Xehanort and Xehanort (a.k.a. "Terranort") as villains.
This is pretty much all but canon. Nomura has said that if the Heartless and the Nobody of the same person are destroyed in that order (apparently it can happen the other way around, but very rarely), the Other is reborn. Xehanort's Heartless (a.k.a. Ansem, Seeker of Darkness) was destroyed in the first game and his Nobody, Xemnas, was destroyed in the second, so that means that Xehanort the person is back. However, in the "Signs of What's Next" ending to Kingdom Hearts Re:coded, Yen Sid says that there will be "more than one Xehanort" returning. There is also a scene in one of the trailers for Kingdom Hearts 3D: Dream Drop Distance that shows Braig confronting Master Xehanort (as in the original, not the Terranort form) at the Hollow Bastion computer room. Braig says "Master Xehanort... have your memories returned?" and in response, Master Xehanort pulls out his Keyblade (as in Master Xehanort's Keyblade) and attacks Braig with it. It's possible that somehow, both Master Xehanort and Terranort will return in Kingdom Hearts III.
4. Xion will make an appearance in a future game.
Remember the "Blank Points" ending of Kingdom Hearts Birth by Sleep, with everyone looking up at the sky and saying "Sora"? Xion was there too, along with Roxas and Axel. According to DiZ/Ansem the Wise, Sora is going to "save" all those people from their fate. What that means exactly is pretty vague as of yet, but if Xion is one of the people Sora has to "save", it means that Xion will probably be appearing again, even if only as an illusion or taking place in Sora's heart (like, presumably, the battle between Sora and Roxas in Kingdom Hearts II).
5. Terra's Lingering Will will make an appearance in a future game.
Nomura has said that, like the battle with the Unknown in the first game's Final Mix version (who later turned out to be Xemnas), the battle with the Lingering Will in the second game's Final Mix is canon. What I interpret this to mean is that the Lingering Will will be showing up in a later game, possibly attempting to retrieve its (Terra's) heart from Xehanort.
6. An instrumental mix of "Hellfire" will be used as the boss battle music for the Hunchback of Notre Dame world in Kingdom Hearts 3D: Dream Drop Distance.
Can you think of any better music to use?
