The Scarpia Ultimatum (http://tvtropes.org/pmwiki/pmwiki.php/Main/ScarpiaUltimatum) (earning: Tv Tropes) is where Character A wants something from Character B (often, to not kill someone dear to Character A) and Character B sets sex as the price.

You know Steve would pay that price to save someone, something, the world...

(Extra points for Skinny!Steve because this anon has a Thing for tiny mouthy fragile indomitable skinny!Steve.)