Board Thread:General Discussion/@comment-6192846-20140111153519/@comment-6986530-20140727213610

It could be possible that only Sloth dregs leave someone without magic talent--or that the lack of or amount of magical talent in someone has nothing to do with someone with demon dregs in them, it just affects how they are around other demons and gives its affected individuals talents. (Although wasn't it that Germaine's healing ability was what Irina was after? While we don't know if Rin or Mikina have any unique abilities from the demons.)

I'm fine assuming it's the Key because of the cliffhanger it was in DoF as I said, but it may be confirmed with a look at the scene and seeing if she tries to take Rin's body at any point.