User blog comment:IamJakuhoRaikoben/Chapter 466: Assassination, Review./@comment-5303512-20151216145356/@comment-7418318-20151217213040

No joking or sarcasm this time around.

I doubt that Brandish would become good due to a subordinate turning on her. At most it might change how she treats other people, though I doubt even that.

There are two possible reasons I can see for her becoming good.

The first is that Zeref or the other Shields betray her, making her realize that what she believed in was a lie all the time, which would require more backstory, since we have barely a clue what she believes or why she follows Zeref, which is possibly also the reason why she hates Layla. Jakob (or anyone else) controlling Marin would fall into this.

Or the other is due to someone from Fairy Tail saving her live. Lucy's the prime candidate here, because she was the one who was humiliated by Brandish. At first Brandish will assume Lucy did it to get information about Alvarez or Layla, which will cause Lucy to have an emotional scene in which she shouts down Brandish and tells her that she did it only to save a life, because of her believes and principles.

With that being said, I doubt anyone is controlling Marin. Why would said person/being know Marin well enough to imitate his ideosynchracies... or bother to do so even if they do? And if they managed to controll Marin and get him into the heart of the enemy, why go after Brandish, instead of doing something a lot more destructive to Fairy Tail, like laying a bomb or assassinating memebers to demoralize them? Or even just spying for that matter.