Okay, pretty simple concept: During the battle, one or both of the fiends surrenders and pleads for their life, offering the Nein pleasures beyond their wildest dreams if they spare them. One or more of our heroes takes them up on their offer.
+The fiend full-on grovels, sobbing, begging on their knees, the whole shebang
+It's genuine- no tricks or deceptions
+Dom/sub
+The fiend thanking them for their mercy at the end