User blog comment:CNBA3/My Big Three Theories!/@comment-25886825-20150219011405

I think you may be on to something with the first theory. It'd be kinda like with a Pandora Hearts pair of characters. The owner of the body's soul was dwindled (or in this case, sealed) enough so that another soul could reside in the body. E.N.D would be the owner of Natsu's body and Natsu's soul was the soul of someone Zeref or even Mavis met before. And E.N.D's soul was sealed into the book after being weakened by Igneel. THAT'S WHY none of the nine demon gates said anything about Natsu's appearance even though according to Zeref he was END. AND the reason Natsu looks normal even though he's a demon is because that is his conservative state (like the other Tartaros members had).So that means...after END is awakened...Natsu might not come back...But if he does, then END and him'll have to share a body with END sometimes being in control. That theory has a few holes though: Who was Natsu originally, how could just the soul be sealed, how was this not found out by ANYONE? Especially Mavis?