Board Thread:Speculation House/@comment-14138255-20160103163552/@comment-26872876-20160103235736

Phantomlink959 wrote: At this point I could see a singular human entity able to control grimm, but no human grimm hybrids.

Yeah, since Pyrrha mentions how people have aura/souls and Grimm don't. Seems the only way for a human to be partially/ffully Grimm would be to lose their aura/soul or partially lose it (which seems impossible).