[ Spoiler Xion was an incomplete replica/shell of Sora made by Xemnas from his memories, it took the form of Sora's most powerful memory (Kairi), as he had little recollection of himself at all. Xemnas' plan was for her to eventually absorb Roxas, and with the components of his memories and his body/soul, "become" Sora. That way they would have a Keyblade Master under their control, and in doing so the real Sora would be trapped in the memory pod forever. Xion is a girl, but as she becomes more "complete" in the end she's to become Sora ]
