User blog comment:IamJakuhoRaikoben/Chapter 503: The Last Sight Seen, Review./@comment-26389992-20160926145116/@comment-24546844-20160926160900

Every demon who affected Gray in some way has been defeated. Deliora, Keyes, and Mard. For what Gray is concerned END might as well never even exist and if he wants to direct his hatred towards someone it should be Zeref. Now, if Gray is stupid enough to throw away one of his best and longest friendships for the sake of mindless revenge then he's just being an idiot.

@CNBA: Natsu isn't smart enough to come up with a way to seal Zeref, he's driven to kill him because that's what he's been programmed to do. And even if he could do something else, Natsu was hellbent on killing Zeref last time even though he was aware of his consequential demise.