User blog comment:IamJakuhoRaikoben/Chapter 415: And It Shall Become Your Will To Live, Review./@comment-24546844-20150110204315/@comment-24546844-20150110215957

I don't know about Acnologia. Maybe what kept him stronger was slaying dragons, but without any dragon to slay he is runing out of fuel and his body isn't able to keep his power. This may have something to do with the soul thing Grandiney said, I'm almost sure that will be brought back somehow when the Dragons Slayers confront him again.

And about Doranbolt, that's exactly what I thought. There's no way to tell if he wipped his own memory or not apart from mind reading or that lie detector thing. I think he won't erase his own memory and will make some research on Lumen Histoire. It would be interesting to see him confronting Makarov when the time to release it has come. I'm betting in Lumen Histoire having some sort of dangerous drawback, after all, the whole "darkness" thing Ivan said cannot be baseless.