Let's say the villain(s) of the week capture on of our super soldiers and while they plan on keeping him alive, they won't set him free until they have permanently ruined his asshole.
So... size kink, object insertion, whatever else you can think of, and lot's of humiliating talk about how they're permanently ruining him.

No explicit scat please. Other than that, go wild. It's not so easy to damage a super soldier, after all.