This is exactly what you were trying to imply. And now that you've been firmly corrected on that front by a couple of people who regularly deal with the legal system here, you're moving the goalposts.
Nobody has said that it is not discriminatory, nor that it is necessarily right. It is, unfortunately, the way things are. Many of these establishments have had negative experiences with foreign nationals and decided not to allow non-Japanese clientele in the future. These negative experiences include violence directed at the providers, poor personal hygiene, demanding service that is not on offer at the establishment, haggling over the price, and various others. Yes, these issues are also occasionally occurring with Japanese clientele - but the argument is that it is easier to handle the Japanese rulebreakers because there is no language barrier, and they have local ties that can be leveraged to ensure compliance. Other establishments (particularly brick and mortar shops) judge that their Japanese clientele would be put off by seeing foreign faces in the shop, and don't want to endanger their core business. We may not agree with these rationalisations, but it is the way things are at the moment.
There is nothing in Japanese law that forbids discrimination on the basis of race or nationality. The Japanese government is, however, signatory to the International Convention on the Elimination of All Forms of Racial Discrimination, and some judges have taken this to stand in lieu of such a law. In 1998 a Brazilian resident of Japan, Ana Bortz, sued a jewelry store for racial discrimination after she was ejected from the shop because of her nationality. She won, was awarded damages of 1.5 million yen, and established this precedent.
You are perfectly free to sue this establishment. To the best of my knowledge, nobody has yet attempted to sue an adult services provider for racial exclusion.
I look forward to reading about your case in the news.
