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blablablub: The main question is; is it really illegal as per local law in Japan.
While entry (only) without permission is illegal, but as per local laws its possible that it isn't really considered a serious/severe crime (unless something is stolen, or have used a forced-entry method like breaking into the house).
Also, calling cops or them reacting to a case relating to a non-permitted entry, is only possible if its a "Man" who is doing non-permitted entry (i mean, would cops really react to any complaint from a guy, if he calls them and say that a woman entered into his house without his permission and went nude).
Heck, even if "i" faced a woman who entered in my house without permission, i would be rather afraid of calling the cops, as i could get in trouble myself instead just by the words of that woman in question (even if the one in the wrong is the woman, because of how the laws are in place).
You have to remember that each Nation has there own laws and views regarding situations, and you can't really compared to your own local law standard (in case of this story, its based on Japan, so you have to consider Japanese local laws).