...It's hard to give a specific source since it's based on my time in Japan, news/news documentaries, and so on. And it's not like I said anything that really isn't a common knowledge in Japan especially to those who've looked into these things.

The story of your personal experience with brothels is not an uncommon one (though on the same token there are many of them know exactly that "waitress" jobs aren't "waitress" jobs but are willing to take the risk to get out of their country) and also I never denied that coerced prostitutes don't exist. Of course they do. They even exist all over USA and Europe.

But I doubt you've been to every brothel (and how we define this can definitely vary a bit in Japan) in Osaka or even met close to 10% of the working prostitutes since many of them don't even work in brothels (you usually call/email them and meet them somewhere usually at the love hotel. this is how it's been done in Japan/Korea for a while now). There are many SE Asians, Koreans, Chinese, (and even Japanese) who are working as prostitutes and yes most of the ones who are working as prostitutes do have sad/tragic stories of their own. But how much you want to believe the extent of story is totally up to your judgment though even if 10% of it is the truth it's a sick tragedy.

You can just walk down Kabuki-cho and other red lights and see plenty of Japanese prostitutes, see plenty of sex service business with Japanese girls, and etc.

And as I've mentioned things like Enjo Kosai (unless you believe it's only the coerced Chinese that's working these as well) has always been a problem and it's a growing problem. It's known many AV stars got their start from cabarets and as escorts (...and you can still hire many AV stars for sex quite easily if you have the cash). And Japan has always had the culture of prostitution... so I'm not sure why you have hard time believing they'd have many of their own as prostitutes.