User blog comment:IamJakuhoRaikoben/Chapter 411: Quid Pro Quo, Review./@comment-4449950-20141201232911/@comment-9595671-20141202124726

If they can, then I have no idea how they due. One could also say due to his magic he was able to weaken it, so the fact he's half black was kinda the consequence in doing that.

And for your theories I vote on #3, mainly because he formed the curse to kill Zeref so no one could take no damage from it.