There's plenty of hentai with rape in it. Every now and then you get one where you kind of wonder at the end. I mean, yes it's probably rape, since he took her without any interest in her feelings. However, it turns out that she likes him.

I'm not talking the stuff where a rapist grabs a random girl, takes her, and she likes it enough to stick around. I'm talking about setups where the guy has a specific target with some history, and he's either so frustrated that he doesn't care what happens to her, or he's seriously mad and wants to hurt her. So he rapes her, possibly punishes, blackmails, or otherwise abuses her before. Then he finds out that she likes him, or at least she's fine with sex and doesn't think of it as rape.

This can end lots of different ways, bad or good. In one case, a guy raped a girl and, right as he finished, her mother called her cell. She answered and said she was playing with a friend and had decided to sleep over. In another case, she took it as an awkward attempt at courtship and told him that if he confessed to her, even after that, she may very well accept him. Sometimes it looks almost like the whole thing, even the rape, was part of her plan to win him.

Of course, if it's an act of anger, the realization that she's into the guy could come too late. In one hentai anime, for example, a guy blackmails his childhood friend who'd assaulted, basically raped him in front of the student council. For blackmail, he uses a video of her masturbating, unaware that she was using his picture to do so. When he finally rapes her, she admits that she has liked him for a long time. Of course, by now the resentment has festered too long and there's no chance after something like this that he'll trust her and make her his girlfriend. He's already decided she'd be his pet.

I don't care what the girl is to the guy at the end, so long as she's his.

Take on me was like that, I think.

Thx. Pretty good. At first when he tries to entrap/blackmail her, it looks like she just loves sex. Once you go a little farther, it turns out that he'd fallen into her trap. One I just recalled is a one-shot by Itou Ei called Sweet Trap, from Shoujo Zukan.
One piece by [m]Kusano Kouichi[/m] comes close. A young woman gives her boyfriend everything short of true sex, because she wants to "savor" his virginity a little longer before forcefully taking it. One day she lets him give her oral, though, and he snaps and takes her, after which she beats him for taking away her opportunity to steal it from him.

This isn't something that only happens in Hentai, and I'm fine with stuff that's less explicit. I remember hearing that near the end of KareKano,

The girl doesn't have to deliberately set him up, or be dating him. It'd be cool to see a girl just admit that she already liked him, and was even happy to let him take her.