User blog comment:FairyRaven/Fairy Tail Chapter 401: Igneel vs. Acnologia, Review and Commentary/@comment-77.194.131.12-20140922125827/@comment-4933386-20140923035726

I reckon that since END is a flame demon, he has the capability to devour to eat flames; which is most likely be Natsu if he attempts to open the book.But then again, if that's the case, Mard would've done it ages ago to eliminate Natsu.