A gal getting a guy to accept being locked and then passing the key on to her sister suggests some great possibilities. How about a series of five caps and, in each one, the key has been passed to another female? Each one, of course, would be crueler than her predecessor.
I am a bit in two minds about key-passing, because it tends to violate the concept of consent - you may notice in my caps that while the victims often end up with more than they bargained for, they DO at some stage bargain for it: there are no instances of guys waking up and finding themselves locked, or science fictional societies where the women keep all the men locked etc. To me, the beauty of chastity is that the locked male is at least at the start a willing victim, and one who has actively participated in the creation of the trap he ultimately finds himself in.
I was thinking of the guy consenting to the initial locking, but not to the key passing. On a seperate note, that cuckolding wife in the last caption is sooo nasty. THANKS.