[@FlitterFaux]

I think that has some interesting potential. A powerful semblance that only targets Grimm? That would go a long way to helping explain why Beacon would take in such a ragged and troubled girl to train.

Perhaps she could even temporarily take over and manipulate Grimm, able to make them fight for her. And then destroy them when she releases them. 

Or she could be inheritly dangerous to them, her semblance could weaken Grimm that stay around her or cause them to become fearful and flee.

Lots of possibilities here.

Personally, I rather like the first one.