Anecdata: a female friend of mine was beaten up by her boyfriend (who was a pimp at a "soapy") and sent me pics of the bruises. I told her to go to the police. She said they would do nothing, something about her dad having a bad reputation (I didn't fully understand her Japanese text messages). I said go anyway and at least try, she's got clear evidence.

She did. They did nothing. And I've got several other similar stories from other women I've known. There is a LOT of unreported domestic violence and sexual assault in Japan.