Two of these really jumped out at me. The ones with a key changing hands are scary and exciting at the same time. Bad enough to have a new girl receive it from your EX. But having it sold to a dominant couple is really extreme. Say goodbye to your old life forever.
As you probably know from previous posts, I'm a bit careful about consent - for instance I don't do those science-fiction sort of captions where women have taken over the world and have forcibly locked all the men, etc. etc. So key transfer can be a problem ... I usually make sure it only happens to guys who made the mistake of insisting that the keyholder had the right to do ANYTHING (like in 2911), or that the key transfer is something the victim willingly accepts (like 2913, where he'd prefer the new girlfriend to have the key rather than the ex). Key transfers are pretty rare in my work nevertheless ... it did not occur to me I had 2 in the same group of 5. I would have swapped one out if I had known; I try to make a group be varied. You're probably aware that I work in advance (usually by 50 caps or so, but it's blown out to over 160 at the moment), so I can always swap one cap with a later one to make a set more varied.
You handle the 'consent' issue very well. At the same time, it can sometimes intersect with the 'be careful what you allow' theme and it's companion, the 'going further than he anticipated' problem. It's complicated... but fun.