The filmed explained
I posted this in another thread, and this is just one interpretation from my brilliant teacher and my film studies class, but it's a pretty solid one:
1. Everything in the last 20 minutes is Aoyama's dream, basically everything after they get to the hotel, she shows him the scar, they are about to have sex. The only "reality" is when he awakens. Then again, more of the film is probably subjective than it may seem, such as when it appears the man working at the restaurant and hearing the conversation about the audition is judging them. He appears later in the film, in the room with the man in the wheelchair. Aoyama fills in all the blanks about Yoshikawa in his mind. In addition, nothing in "the room" with the phone and the man in the bag is real. There are many dream sequences in the beginning, and they are meant to be jarring. As is the scene that Aoyama's friend is trying to talk him out of seeing Yoshikawa and there are tons of jump cuts.
2. Aoyama seems like the nice guy, but is he really? Think about how he speaks of women. He says he wants someone confident, but he's infatuated with the obedient, passive girl. He held an audition to pick out a wife, asking and listening (from his friend) to a number of pretty degrading questions. Then he chooses which one he "wants". Do you see the darker misogyny and misuse? It's something that's laughed about in romantic comedies, the way women are treated. But this film examines it from another angle.
3. He doesn't treat any of the women in the film well at all. He's pretty rude to them, actually. His secretary, who it's hinted he's slept with and ignored. The girlfriend of his son. Really any woman he comes in contact with.
4. The dreams, the fears, are his projections. The sickness of them...perhaps his own sadistic sexual desires. For example, When Yoshikawa opens her legs to be burned by her abusive uncle, we see her both as a little girl and as an adult. The tongs are a phallic symbol, and there is a sensuality about the way she reveals herself willingly. Several things "happen" when she is a child, then an adult, then Aoyama's late wife. And remember when the son's girlfriend is giving him a blowjob in the dream, and at first he succumbs to it, but then pulls away all "This is wrong, this is wrong"?
5. His opinions about life (Enjoy the pain, that's life...which comes back to haunt him in the dream sequence....Life is beautiful) contradict, as again do his views on the ideal woman.
I don't think the film is a warning, I think it's a reflection on the role of women in Japanese society and how they are viewed/treated, as well as the concept of the female as the monster put into question.
Who is really the monster here?