One thing eludes me about the Japanese porn culture. Why the girls allways got raped and why they always love it!?
Sorry for the big text. xD
As to why they got raped, its the same as all country. There is no reason why the are raped... An horny scum (man or woman) who can't control his/her sexdrive... (this kind of guys/women are at the same level of mindless animals)
As to why they end-up loving it... It's the brain trying to save what it can from total break down.
I like to take the exemple of "vertigo" to start with the goal to illustrate the power of the brain and show/explain why they end-up "loving it".
(Vertigo - green part)
vertigo... It is the brain which races and says "Attention, danger!" but the rest of all the senses ( sight, hearing, touch, etc.) say "No danger!". And the brain doesn't like paradoxes at all. And sometimes he takes drastic measures to sort out the paradox... In the case of vertigo, to make sure that the senses and the interpretation that the brain does is in sync. He can basically say to you "You want to jump." ... And you will jump. (the brain can be extreme in its way to solve this kind of problem...) Well, technically, he will make you create a situation where you are really in danger if you can't go back and make distance between you and the "source" the brain consider like a danger.
In the case of rape it's somewhat reversed, the brain interprets it as "mentally" unpleasant. (no one really likes to be raped --> maybe the ones who fantasm on it but I can't be certain since I'm not one of them) But on the other hand, the human body is made to love that, to love reproduction... Whether we mentaly like it or not... And the brain can do nothing about it... He receive physical information saying "pleasant" but it interpret it as "unpleasant". And he can physically do nothing to change that... Which creates a paradox ... And the brain does not like paradoxes, as I already said... Then, to synchronize the mental feeling and the physical feeling, it will make the decision to "bend" the person's mind by making them believe that they like it. (in short, it "say" to you "You love that." and you end-up loving that) It's a way to preserve the mental sanity as a whole... (and potentially save you life ---> by resisting, maybe you will end-up killed... but by becoming "docile" you increase you chance to be spared ... By asking for more, you make your agressor in a mood to let you alive --> it can be called a survival instinct, at this point)
We tend to use "mental break" as a tag for hentai. But it's more accurate to say "Mental Bend". Well, in hentai, the effect are generally definitive so "Mental Break" is still good. But in reality, the effect are most of the time a short term effect.
And to trigger this kind of mental bending, it's not with one go but with repeated rape for days or even weeks... (depending of the mental strength of the woman) This kind of case are relativelly rare. (for the common of victim / rapist) So, it happen rarely. But it's possible.
Another exemple: It's similar to some case of tortured men/women who laught while they are the victim. The brain try to preserve the majority of your mind from complete breakdown by bending a part of it ... by doing that.