Public opinion shaper and universal concept.
Japanese movies, drama, animation, and so on seems to be not the appropriate way to judge Japanese opinions, especially their morals.
Considering the fact that the entertainment industry seems to be part of the shaper of public opinion instead of the other way around. The normal Japanese themself wouldn't like to be associated with anime, what make you so sure that the Japanese adopted the believe represented by this medium and others?
As for serving under the winning side. Well... When you're in a house, it's better to follow the rules of the host. A change of host, a change of rules.
As for "'wrong/evil' only exist as long as it causes bad feelings or damages to other people."
Universal concept, good concept, but the Japanese don't hold a monopoly on this one, most of the world practice this concept, even those who stayed in 'western' and 'muslim' countries.
Unfortunately, the Japanese or at least those who are afffected will no longer hold or practiced this universal concept,due to public opinion shaper, including the one above.
As for the girl who slept with 12+ guys.
Either she is really frank (almost to the bordering of psycho) or she is just a figment of someone's imagination. Of course that depends, did she said 12+ guys after she was asked or did she said it on her own?
Girl in general don't disclose their sexual nature openly. Society rules? Could be, but the other thing is that, the secret or the disclosure of a girl's sexual nature can be exploited for the girl's own advantage, and a girl can be quite good at this sort of thing.
Imagine a girl is like a car. While you might a capable car that perharps that had been driven for quite some distance to prove that the car is quite capable, you don't necessary want to see the odometer to see on how much the car have travelled, unless of course you're the safety concious type of person that need to know everything.
Anyway. If she said that it's okay for her to slept with many different men because she's always tell them the truth, she's right on not hurting anyone.
On the other hand, there's the issue with her parents, do they approve of her doing this sort of thing? Wouldn't be kinda degrading and hurting to the parents if the parents were hurted by her actions and she said that she didn't hurt 'anyone'?