I made friends with some Yakuza while I was there, and after awhile I would get invited to some of these places sometimes. You REALLY need to be careful hanging around them though, and don't get dragged into their shit. They usually keep that separate, but it's not guaranteed.

Also, you're expected to be on your BEST behaviour. DO NOT EMBARRASS PEOPLE, because the responsible person will suffer for it (not you, but please, don't be a dick).

Actually, if you want to get a peek at what the underbelly looks like (with a lot of creative license of course), check out "The Naked Director". It was quite refreshing compared to the regular pablum of Japanese television.