User blog comment:IamJakuhoRaikoben/Chapter 451: Fairy Heart, Review./@comment-26263257-20150907085505

So Hades plunged into darkness in his pursuit to revive Mavis and "fix" everything. Perhaps he still had some Fairy Tail in him, and he secretly hoped that Fairy Tail would defeat Grimoire in Tenrouj. I think Natsu unconsciously tapped into his Etherious power in developing a spell that can potentially kill Zeref.

I predict Alvarez to run roughshod at Ishgar's primary defensive lines, and force FT to use Fairy Heart. Natsu kills Zeref with his etherious power, and END manifests after... forcing Gray to fight Natsu and landing a critical hit on him... Fairy Tail members are plunged in state of internal war again over this... for some reason, Juvia decides to go against Gray since she notices that Gray has been consumed by revenge... and Fairy Tail decides to join together and "save" Natsu from his END form.

...and then an arc later, we hear news of Acnologia's sudden death at the hands of the series-ending villain who we still don't know about (probably Anksheram)...