First I was drawn to most of these keyholders being naked. Their casual nudity would certainly add to the chaste one's torment. Secondly I enjoyed that some of them had come up with creative ways to use a slave's mouth, for giving a tongue bath to her butt or being assigned 'bathroom duty'. So many possibilities.
I try to mix up the nudes, the semi-nudes and the non-nudes. Each presents interesting challenges to the 'story' I see in the pic. Is the girl the keyholder? If so or if not, what is her relationship with the victim/reader? Does that match her state of dress/undress?