MY xion theory

[Genocide]

Just to go back to the whole "fake keyblade" thing...

How do u fake a keyblade? Also Riku said it was a fake. Did he really know or did he just assume it was a fake because he didn't know of any other wielders other than himself, sora and roxas?

Well, the only confirmed fake Keyblade is the Heart Unlocker from KH1.
Since his Keyblade is real, he'd know what a fake Keyblade feels like, since he's used one before.

If we assume that Xion's Keyblade might be - much like she herself might be - made up from Memories that leaked out from Sora/Roxas

Remember my last theory - Active Keychain.....

that possibly latched onto an existing ability (this would be where I'd strike out Aqua relations, but I can't do that no more), it would make the Keyblade to be a fake.

No Aqua.