User blog comment:IamJakuhoRaikoben/Chapter 438: The Seventh Guild Master, Review./@comment-24039234-20150601171314/@comment-7418318-20150604075122

She doesn't need to become evil. She could just go through something similar as Yuriy in Zero. He didn't actually become evil either, but his real self was kind of pushed back into the far reaches of his head while the stored up evil stuff in the Tenrou Jade controlled him.

Shadow taking over Rogue's body was also similar.

I can see E.N.D. doing something similar to Mirajane until the Demon's mind is sufficiently weakened by being beaten for Mirajane to subdue or exorcise it for good.