It has been stated that Sora was not alive or a being till Ventus was left on the island. Point blank he was not even born. Only till their hearts conected was Sora born. Their is a high chance Sora could be Ven light half that chose to stay conected to Ven to keep him alive. After all Merlin said he was only full of light. While Vanitas was born of his escaped darkness. If that should be true than Sora is in a odd way,the child of Ventus or half of him as is Vanitas. After all Ven's heart was unlocked, and thats how Vanitas came to be. So who's to say the light part didn't also have the chance to be free. And considering BBS, and dream drop, Vanitas is the key since he's the only one that can remember anything involving Sora and Ven.
