I'm sorry, but calling nyotaimori a "quite common" Japanese "ritual" or "tradition" is really stretching it. As I recall (sorry, can't find a source right now, and it would in Japanese anyway) nyotaimori was dreamed up less than 10 years ago by a ryokan keeper desperate to find a way to get more customers to his lodge way out in the boondocks. A somewhat sensationalist Playboy article in 1999 alerted the world to its existence and now nyotaimori seems to feature prominently in the fantasies of anime otaku everywhere...

At any rate, nyotaimori quite literally means "female body plate". The crotch is covered with shiso leaves and attempts to poke at it will result in the plate's immediate departure. In all, the whole idea is really rather silly: heating raw fish to 37 degrees and giving it a fine coat of sweat is unlikely to improve the taste. If you want to see a naked woman up close, you can go to helluva lot of strip bars for $1000, not to mention get laid. On the other hand, I doubt Japanese feminists give a fig about this, nobody is forcing women into being platters and much worse goes on daily in the murky depths of Kabukicho.

Incidentally, a Japanese language web search for nyotaimori will turn up a lot more links to Nyotaimori The Thoroughbred Enkacore Crew, who evidently combine enka with hardcore punk and seem to be quite popular in the Japanese alternative scene.

See http://www.multimania.com/isgtokyo/actua/nyotaimo/nyotaimo.htm for a French version of the Playboy article, with the original pictures.