What i think is that Xion was made by Namine out of the memories of Kairi and Sora and that is why Xion looks so much like Kairi and can use the Kingdom Key. This could be why Riku said that her Keyblade is a fake. Also Namine could of made her just to keep an eye on the Organixation and maybe why Xion said that she would Disappear.
What do you think?
What do you think?