quote Blade_Runner

Wow, never thought of it like that. Everything in your story matches up, but if this actually happens im going to get pissed.

Why?
This theory is not only believable, but it's interesting, too!
It's like Invasion of the Bodysnatchers, Kingdom Hearts style!

Although I just realised a problem, Jon24hours...
You didn't bring Kingdom Hearts (the moon-thingy) in anywhere in your theory!
It's shown in the vid at the end of KH2 when MX and Vanitas are destroying Terra, Ven and Aqua
It's made obvious that Master Xehanort is interested in Kingdom Hearts(moon-thingy), so we'd need to figure out how that's related to him possessing Terra

Well, here's another theory for you, then:

The name "Xehanort" is not of a single being. Rather, it the the one that a being remembers after a strange phenomenon. Master Xehanort, being the current Xehanort, finally realizes what is happening and is willing to do whatever is needed to become whole again, targeting Kingdom Hearts. However, in order to do that, another "Xehanort" must be created.

Vanitas isn't a person at all, rather, a being created by Xehanort's power, explaining why he has a Keyblade and why he separated from Master Xehanort during the secret ending of KHII.

Master Xehanort teaches Terra to use the power of darkness, using the excuse that it will help him become a Keyblade Master. However he eventually realizes that he want to use his powers to help his friends, rather then to be a Keyblade Master.

Master Xehanort then goes after Kingdom Hearts, with Terra, Ven, and Aqua on his tail. Vanitas and Xehanort gain the upper hand, and Xehanort rises to Kingdom Hearts.

Terra, being the only one left, with Ven frozen and Aqua grieving, goes up to face them. Though Terra defeats Master Xehanort, he finalizes his turn into Xehanort, with Vanitas going inside of Terra, wiping his memory and turning him to the darkness.

"Xehanort", now with no memory, becomes Ansem's apprentice. His power hunger as Terra now had no direction what-so-ever, with no friends to fight for. He begins his study of the heart.

Figuring he needs a younger body in order to gain more power, he targets Riku, and tries to turn him to the darkness, by sending him through a corridor of darkness to Maleficent.

In order to stop Xehanort, Ven and Aqua go inside Sora and Kairi respectively, and with Ven knowing Sora knowing he'll stop at nothing to get Riku back, and Aqua knowing Kairi is a Princess of Heart and can provide back-up, Sora sets out.

When Xehanort is blasted by Kingdom Heart's light, he was not destroyed, rather, purified, transforming him back into Terra. He then waits for the next Xehanort to rise, possibly foreshadowing that another strange phenomenon that created Xehanort in the first place will happen again.


Another theory to look over. What really sucks is, certain plot points are missing, causing holes in any theory that appears. Such as, it's said that the Xehanort that looks like Terra appeared after a huge Keyblade battle. Another Keyblade War, perhaps? Is it possible that once that many Keyblade Wielders appear and begin slaying each other, Xehanort is the byproduct? Is it possible with Sora, Kairi, and Riku, that the cycle is over and Terra is waiting for nothing?

Yeah, I suppose there's little chance of guessing what'll happen before the game comes out
But some parts of your theories make a lot of sense

Xehanort (Ansem's apprentice) does look like a cross between Master Xehanort and Terra so I think that'll be important

The whole bodysnatching thing is very different for a Kingdom Hearts game, but maybe it would explain the title
Birth by Sleep could mean the 'birth' of new Keyblade Masters by having Vanitas, Ven and Aqua's souls 'sleeping' inside them, waiting for something to happen

Or maybe they'll reveal that Sora is a patient in a mental hospital and the whole series has just been a figment of his imagination...