I've spent a significant fraction of my time in Tokyo over the past couple of decades, in visits ranging from days to months and have sampled the Japanese commercial sex scene fairly broadly. DW98's experience is clearly more extensive, but I know enough to say that his FAQ at the top of this thread is really excellent and should be invaluable help to any gaijin looking for p4p in Tokyo. I'm happy to add my bravo and thanks to the others above!
I'd add only one caveat: The extent to which you can partake of all the wonders of the Fuzoku world DW98 describes will depend A WHOLE LOT on the extent to which you can communicate in Japanese. It is easy to underestimate, or understate, how important this can be, and for someone (like DW98, apparently) whose Japanese is quite functional, it may be easy to forget how crucial it is to their experiences. Even a few words of the language (if they are the right words) can make ALL the difference between a commercial sexual delight and jerking yourself off in frustration back at the hotel.
And, even beyond the simple issues of communication, it will help you get into places if your behavior appears polite, controlled, calm and somewhat passive (by Western standards). To be clear, I am not talking about your behavior in private with your commercial sex partner but about your behavior "at the door or front desk", so to speak. One of the major reasons that Japanese sex (and non-sex) businesses sometimes refuse to do business with gaijin is a fear that the foreigner will get angry, upset, excited or whatever and "cause a scene" and a disturbance, perhaps due to not understanding "the system" or what is happening. Not being able to communicate with the person well, or at all, of course increases this apprehension, but even if you don't speak or understand a word of Japanese, you can still help your own cause by not appearing loud, demanding, excited, confused, uncooperative etc.
-Ww