I just noticed too how many hits this thread has. Wow. So I thought I'd chip in with a couple of examples I know of from the world of JAV. Someone already mentioned Mourning Dress Sisters.
Aroma: ARMD 196... this is a very strange movie as befits the subject. Mother and daughter sex. They are the only two who appear in the movie. There are basically two long scenes, with the first starting while the daughter kneels at a table and the mother serves her breakfast (I assume as the daughter is wearing pyjamas). The dialogue might help to know what's going on but the mother could be saying "please eat your cheerios" in a low key way, smiling and talking and yet somehow it just develops into a scene with the mother "seducing" her daughter. The daughter never talks or really smiles but seems at once puzzled, dazed, aroused, unresistant and willing. The second scene continues in a dreamlike way with a long scene in bed. I guess one reason this movie didn't do a lot for me .... it was very heavy on the saliva fetish. Now there you go, an incest fetish combined with a saliva fetish.
I really like the younger actress who I've seen in other JAV lesbian, though I don't know her name, and the older female was a "perfect" mother figure. Not unattractive, not as slim or lithe as the younger female and therefore a good contrast.
It ends with the daughter lying in bed under covers, "waking up" as if from a dream with the mother sitting by her side with an air of concern on her face, and a moist towel on the younger girls forehead to suggest she's come out of a fever.
Well I guess that's one way to deal with the subject. Marks for concept.
SOD Create - another one, that is a "drama" something like Mourning Dress Sisters but darker. Too dark for my tastes but nevertheless fascinating too. Kind of hard to balance dark drama with hot sex but there you go. One moment you're thinking ah how sweet, the one cute schoolgirl jumping out from behind the signpost to scare the other pretty schoolgirl ... with plastic fangs in her mouth! The one who was supposed to be scared is too deep in thought to have noticed and it's endearing how they interact. You're jerked back a few minutes later when the one with the plastic fangs commits suicide after a scene where they've had a very intimate sexual encounter. I don't mean intimate just in terms of what they do but it's portrayed as the one girl in love with the other and so her suicide is meant to represent what? Rejection? Anguish? Wait a second here.
Anyway, it gets stranger if that can be. Before the two schoolgirls made love, the one has witnessed from a conveniently slightly open door, a teacher seducing her friend. She has watched in secret with a look of fascination and repugnance until the scene ends with both the teacher and her friend realizing she is watching and looking directly at her. After the suicide, she visit the home of the teacher ... here I'm lost. I don't know what the relationships are but the teacher has a photograph of the girl who killed herself and perhaps it was her own daughter? Anyway, the teacher seduces the schoolgirl who heads home in a daze. For some reason, she follows her mother the next day and trails her to the teachers house. Again, she spies on people and see's her mother and the teacher engaged in a passionate scene. And this time she is drawn into it and ends up having a "three way" with her mother and the teacher.
I'm afraid to say this scene ends with the mother and teacher committing suicide. And the young schoolgirl wanders away in a daze until coming to some train tracks where she is last seen walking along them into a tunnel.
After saying all this you're wondering why I'm telling you about this movie. Well I gotta tell somebody I suppose. It's something you'll either like or loathe. In terms of drama and realism it's hard to beat JAV for things like this, and the sex is very good in places. The initial teacher student seduction is perhaps my favourite but the last scene is also good. The theme is touchy, the presentation is dark and tragic, the actresses are utterly believable, the sex is intense, and it includes mother daughter so it fits in with the thread.
Link to this title cover and scene pics: http://www.raku2-gate.com/site/adult/item/sod0010.html