User blog comment:Renkrisb/The Dragneel Brothers/@comment-64.134.184.169-20150519191607

I F-ing called on it. My original theory:

Natsu was a childhood friend or brother of Zeref (Confirmed) Died and Zeref, in grief, brought him back with Dark arts and resurrected him as a Demon (Half-right, his death was what inspired Zeref to originally diverge into life and death and ended up turning him into the infamous Black Wizard) I came up with this after Minerva was turned into a Demon, and Silver, before finding out he was resurrected with Keith's curse revealed how the material in Hell's Core (I guess ethernano or whatever) could turn humans into Demons.

I'm guessing extracting whatever was put in them is what turns em back into humans (Could explain how Minerva returned to normal in the span of a week)

Last theory regarding Igneel and Natsu. At some point, Natsu and Zeref were wandering and confronted Igneel. Both him and Natsu fought, but Igneel couldn't deal the final blow (Something tells me Zeref intervened) So the two made a deal: Zeref agreed to take out the parts of Natsu with END in it including his memories of his own brother. Igneel would train Natsu to become strong in order to kill Zeref, and if Natsu failed, Zeref would unleash E.N.D to properly kill him. That aside, does anyone else feel a comparison between Zeref and Korosensei from Assassination Classroom?