It's non consentual S**, not always ra**.
These both are pretty much the same but no you don't have to like really ask your Partner before doing it, but if they say no (aside from if they're both into doing it even though the Partner says no) then it's ra** (you can't really describe from what point it's ra**, just Listen to what your feeling tells you and if you're uncomfortable with how the scene goes you should drop it and not force yourself to read/watch it.)