TBF, part of those blanket "No foreigners" ban signs on the places in Kabukichō are due to how central that place is in the middle of Tokyo + tons of tourist traffic, along with Japan's laws on prostitution and their worry about foreigners (esp. ones not fluent in the language) fucking up and turning what would be considered a legal act in Japan into an illegal one.
Basically, prostitution is "illegal" in Japan, but there are a lot of loopholes that allow you to skirt the law and legally pay for sex, basically. It's illegal to pay a stranger for PiV sex in Japan according to the letter of the law, but it is not illegal for "acquaintances" to pay money for any non-PiV sex act. So there's a bunch of different brothel types that do different shit to meet the legal definition of becoming "acquaintances" first. If a foreigner is completely fluent, many places that say "no foreigners" can be convinced to make an exception.