Board Thread:General Discussion/@comment-6192846-20150326001739/@comment-6986530-20150401202734

I think thematically it might be important, but in the context of the story it's just a coincidence. The fact that Yuzette did not die by the Golden Key proves that the key is not necessary to kill a host, it's as simple as that. It might be considered the most useful for killing one, but it is, beyond a doubt, not the only thing that can kill a contractor.

For the record, the implication is that the demon is actively protecting/healing its hosts and that's why they're invulnerable--whether or not Riliane was permanently changed by being possessed, the demon was not around to heal her anymore and so she died by natural means as a result.

It's possible there is a power hierarchy for the demons that makes it so one demon can kill one contractor but not vice versa, but that's speculation. Lemy survived getting shot in the heart because Gumillia didn't kill him with a vessel and/or was not contracted to a demon.