User blog comment:Miskos3/Fairy Tail 515: I Am You...You Are Me, Review/@comment-7418318-20161221082005

Even the genius magician that invented Dragon Slaying was unable to return to her Human shape without help from Zeref.

Does that mean that Zeref really was involved with Acnologia?

I wonder if Zeref tried to turn Acnologia back to Human to stop his rampages, but instead enabled Acnologia to shift between Dragon and Human for at will instead.

I also wonder if that means that Irene can also switch between forms but just chooses not to change into a Dragon due to all the torment that her Dragon transformation brought down on her in the past.