User blog comment:Renkrisb/The Dragneel Brothers/@comment-26416024-20150519215248/@comment-1776824-20150520163306

But if Igneel chose not to kill E.N.D., which believe it or not is actually the case (you can't dispute several different translations that say this, albeit with varying word choices), then that would mean Igneel was stronger and had the opportunity, but elected not to.

Inventing something doesn't necessarily make you strong, and E.N.D. was designed to be the strongest Demon, but I'm more starting to believe that this doesn't mean strongest off the bat, but rather that it involves growth potential. Even though I believe that Natsu's power as E.N.D. is inside that book, I'm also fairly open to the idea that as little as none of his actual raw power is inside that book and just his memories on how to use his old curses and other magical abilities. Using Zeref as an example, legends write him as the most vile wizard to have ever lived and that he took lives for fun and created these magical beings that are known as the Etherious for havoc, however in reality he was punished loving his brother and resorted to every means necessary to end his own suffering. I'm more starting to imagine E.N.D. as like the fat Majin Buu, because accounts of the truth can be skewed and misrepresented. Also, remember that Zeref said on Tenrou Island that Natsu wasn't ready to kill him yet, implying that even after all the time that's passed, Natsu still hasn't gained the power necessary.

Acnologia's is up to interpretation though. I'm less open to the idea of him fearing E.N.D. and more open to the part where he used it as an excuse to go wild, because he himself stated that he wants to destroy everything, and then Zeref himself later said that he does so little of it (for whatever reason). Also starting to wonder how he even knew where Tartarus was.