*Spoilers start here*
She is not actually a Nobody, but a doll created da Xemnas from Sora's leaked memories. Her face was based off of Sora's strongest memory, Kairi, but as Naminé pieced together Sora's memories, she began to physically look like Sora.
The plan was for Xion to eventually become a complete Sora replica, due to the fact that Xemnas was unsure if he could rely on the actual Sora to gather him enough hearts for Kingdom Hearts. Eventually she would have had to absorb Roxas to become whole, and if that were to happen, the original Sora would never awaken. Eventually she is absorbed da Roxas instead, thus giving him the ability to duel-wield.
*Spoilers end here*
In my opinion a completely original storyline.
What do te think
Hint 1: (Namine) "Roxas, do te remember what your true name is?"
Hint 2: Roxas cried at Xion's ending moments
Point Out: "True name" she is referring to Ventus, Roxas' original being before his cuore was put to sleep within Sora da his choice.
Point Out: Ventus' cuore was separated from Sora and put into his Nobody.
domanda for BBS: If Ventus saw what Vanitus looked like before Ventus was possessed the why stay with Sora?
domanda for BBS: Vanitus has two Kingdom Keys fused and equipped with a spear? Why?
Point Out: Both Sora and Ventus could use the Kingdom Key but within Ventus' body the dark key has been removed of all traces of darkness around it. (Ventus seems to be Sora's good half...)
Hint 2: Roxas cried at Xion's ending moments
Point Out: "True name" she is referring to Ventus, Roxas' original being before his cuore was put to sleep within Sora da his choice.
Point Out: Ventus' cuore was separated from Sora and put into his Nobody.
domanda for BBS: If Ventus saw what Vanitus looked like before Ventus was possessed the why stay with Sora?
domanda for BBS: Vanitus has two Kingdom Keys fused and equipped with a spear? Why?
Point Out: Both Sora and Ventus could use the Kingdom Key but within Ventus' body the dark key has been removed of all traces of darkness around it. (Ventus seems to be Sora's good half...)