You make a theory based off of what's there. You can't just make stuff up to fit something. I can say Sora loves bananas as a theory, but that doesn't work because nothing in the series has hinted his love of bananas. What i can say as a theory is that the box might have something to do with Sora because MoM has delibaretly been passing the box through Luxu and waiting for something. Whatever that is could be Sora. That's a theory (a stupid one) but the gist is, what you are writing is fanfiction, not theory because the whole thing relies on a concept that doesn't exist in kingdom hearts.