So, post-Civil War, Bucky's trigger words to turn him into the Winter Soldier have been taken care of. However, the HYDRA cell that has captured him and Steve doesn't know that, and they order him to rape and torture Steve while they watch. He and Steve need to keep their cover and prevent the cell from suspecting anything if they want to get out alive with the intel they need, so they go along with it. They're both on the same page there, but it's still awful.
Bonuses for:
Bucky and Steve both being ruthlessly pragmatic about the whole thing while it's happening (Bucky making calculations about how much damage he can inflict without incapacitating Steve beyond his ability to fight, etc.).
Bucky and Steve aren't actually together at this point (whether they were in the past, or even are interested in it at all, is up to the writer).
+10000 for the pair of them ripping a bloody swath through the facility the first chance they get
Steve/Bucky, undercover, fuck or die
Bonuses for:
Bucky and Steve both being ruthlessly pragmatic about the whole thing while it's happening (Bucky making calculations about how much damage he can inflict without incapacitating Steve beyond his ability to fight, etc.).
Bucky and Steve aren't actually together at this point (whether they were in the past, or even are interested in it at all, is up to the writer).
+10000 for the pair of them ripping a bloody swath through the facility the first chance they get