User blog comment:IamJakuhoRaikoben/Chapter 451: Fairy Heart, Review./@comment-1359322-20150907062920

So Fairy Heart is basically a battery that can't run out of energy. Yury died knowing nothing. Zeref wants Fairy Heart to beat Acnologia, so i assume he can't beat Acnologia. Natsu's new technique, probably just some usual destructive spell. Unless of course he subconsciously used the Curse Power his fellow Etherious uses to create that technique.