User blog comment:CNBA3/My Big Three Theories!/@comment-67.149.177.130-20150217175104

Problem with the 3rd theory is that Etherious demons are created from the Books of Zeref. I do agree however that E.N.D's powers and memories and possibly personality were sealed in the Book of E.N.D. though. I see Natsu as just a shell of E.N.D.