If they know where you live, is it really Fetish Freaks Anonymous?
It's probably one of those crank letters you can send to someone. A real organisation would probably have used Presorted First Class (no postmark) instead of an actual stamp. The organisation is supposedly located in Washington but the postmark says Boston.
Why would they actually keep you anonymous? It's not like they have to tell the truth or anything.
The Japanese is really bad :(
I'm glad it's not just me being stupid.