I guess to me, what bothered me is not so much that she gave up her humanity, but that I sensed an implication that the only way to take control of your life is to give up your humanity, that a woman who tolerates no abuse must be inhuman.
Maybe women in Japan feel that way? They may feel like they only have two choices: tolerate the abuse or become a manipulative "demon." I'm not very well versed in Japanese culture, so I'm really just guessing.
I don't think that feeling is unique to Japan. I've spoken to several women in America who have told me that they feel that they have to become "bitches" or act "mean" in order to succeed. In my opinion, it's a combination of truth, perspective, and trauma, but its certainly a phenomenon.
Truth: It's a hard world out there for women, who have to fight against a lot of destructive ideas and assumptions.
Perspective: Socialized to be "nice," lots of women perceive themselves as acting "mean" when they are assertive. Used to "nice" women, lots of men perceive perfectly nice assertive women as "mean" or "bitchy."
Trauma: It is very easy for people who have been victimized or abused to become their abuser. This can be as true of groups, culturally, as it is of individuals. I sometimes think that a lot of women who seem to justify genuinely cruel, bitchy behavior with "it's a man's world - you need to be mean to be successful" are just acting out the abuse they've suffered.
That said, I definitely think there's room to criticize the story's choice in terms of power and sexuality. There's nothing
wrong with a story about a girl claiming her sexual power and other power with it, but with that choice comes the danger of limiting the story to sexuality, making it too titillating and insufficiently real. However, in this case, I think that the story avoided that pitfall with characters who were real and sexual situations that were genuinely uncomfortable, rather than appealing.