qòóp wrote:I've heard that there are clubs in Japan where Westeners can't get in because they would scoop all the girls from the local guys. Selbstverstandlich I find this very interesting

, has anyone heard anything about this?
I don't know for sure, I'm not someone who usually goes to clubs and certainly not someone who cruises for girls. What you say would not surprise me though. When I was there I was told 5% of all marriages in Japan are between Japanese girls and foreign men, which is quite a high percentage.
But...I did have some western friends who would go down to Roppongi (one of the major nightclub "entertainment" districts in Tokyo) and have no trouble picking up Japanese girls and taking them to what is called a "love hotel" where you can pay by the hour...
Western men are often seen by Japanese girls as a better prospect than Japanese men and you will often see these girls in western bars looking for victims

...I spent a while there dodging their claws.
Foreigners are tolerated in Japan, but only as for as long as they are useful. Guess who will always get the blame first if there is a problem? I remember in Otaru in the north of Japan, all foreigners were banned from going into the onsen (hot spa) because they said too many Russian sailors would go there straight off the ships and not wash properly before going into the spa.
Also, they don't like tattoos, so you have to cover them up before you go into the onsen, or they won't let you in.
In most large towns and cities, most nightclubs, bars etc are gathered into one or more "entertainment" district(s) which will cater for all sorts of, well..."entertainment" tastes. There will be a man in a dark suit outside each establishment (probably Yakusa - the local mafia) watching over pretty girls giving out leaflets trying to pull in people from the street...and there will be many of them down each street.
You might be interested in reading Murakami's novel "In the Miso Soup"...it goes into the seedy side of Tokyo nightlife, but don't read it if you are of a nervous disposition as it is a horror story and quite graphic.