User blog comment:IamJakuhoRaikoben/Chapter 503: The Last Sight Seen, Review./@comment-2214433-20160926122428

I'm gonna hold off on judging this chapter until more is perhaps revealed, because this could eventually become the WORST development in all of Fairy Tail. You thought Silver going back and forth between a demon and a father was bad? You thought Erza vs. Kyouka was ridiculous? Well, behold something that is fuckton times worse than anything you've seen: Natsu transforming into some kind of a demon-monster. Because that would be the biggest retcon in all of the manga. Ya know, it's rather tiresome going from Mard Geer's lies to just a little bro being resurrected, but wait *one shots Dimaria*

However.

This could actually be pretty interesting, depending on how it's approached. I very much liked the idea of the cause being Zeref making a hole in the book of the E.N.D. back then. Also, Natsu is Etherious, so him releasing the energy of a demon isn't all that farfetched. That is accompanied by the scene of Natsu searching for Zeref, as we all know, that is the 'homing instict' of Etherious.

So yeah. This could either be good or absolutely disastrous.

Also, I hope Gray stays in character and doesn't try to wreck Natsu. If he ends up fighting him, I hope it's to bring him back to his senses, not because his daddy told him to do so.