I mean think about it: if a foid had a knife to your throat and you woke up, you would be within grounds of self-defense to stab her with that knife and she's dead.
If however you spend the time learning self-defense skills, you can disarm the knife without killing her, leaving her better off as a result of your efforts.
Due to your efforts learning self-defense, she essentially owes your her life, yes?
At this point, if we say that it's justified to take her entire life (killing her) in response to her being about to kill you (trying to slit your jugular in your sleep) then it should be justified to just take a moment of her life (let's say 3 minutes, you'd coom fast due to adrenaline) for some sex.
This is taking much less than 1% of the time you would have taken from her by killing her, which would've been years or DECADES of remaining lifespan in many cases. Rare exceptions made for "I have 1 month left to live due to terminal cancer" type murderesses I suppose, but even then, 3 minutes is less than 1% of 1 month.
So raping a kunoichi who tries to kill you in sleep is basically morally justified as a lesser consequence than killing.
I know a lot of self-defense comes down to "necessity", and I have a counter to that as well.
What if you were so distraught about your life (near-suicidal) that you normally couldn't fathom the idea of defending yourself from a would-be murderer?
BUT what if the idea of getting sex as a reward for self-defense could motivate you to apply the effort needed to defend yourself?
In that case, raping your would-be assassiness is 100% necessary because the thought of raping her is the only thing giving you the strength to disarm that dagger she has aimed at your heart.
Knowing "soon as I stop this knife penetrating me, I will penetrate this QT with muh dick" is your reason-to-persevere.
Obviously this isn't a universal defense: it should not be okay to argue "I had to rape the waitress because thinking of raping her was the only thing that motivated me to stop the timberwolf from eating me in the woods"
It really only works when the subject of the hypothetical rape has taken an action that justifiably forfeits their right-to-life, such as engaging in attempted unjustified homicide against another person. In that instance, anyone trying to stop that unjustified homicide should basically be allowed to rape the attempted-murderer.
This shouldn't be allowed on justifiable force though. If I'm walking down the street and nigra A tries to stab me to take my wallet and I try to kill Nigra A in defense, Nigra B is not justified if he tries to rape me after defending his buddy from me: because my violence towards Nigra A was justified by self-defense.