I work at JAV Bucks a Japanese Niche adult video program. We can convert your traffic from Japan and China also Feel free to contact me leroy at javbucks dot com.
Japan is very difficult to break into, as they have a distrust of anything they deem foreign. I'm a fluent Japanese speaker, but I still have problems getting people to just talk to me because I'm not really Japanese, and many of them assume that foreigners simply cannot understand anything about Japan (language, culture, etc.) no matter how hard they try or how long they live there. Now, the Japanese are amazing people, but it's very hard for an Internet marketer to break down that inherent barrier. I actually don't know of any Japanese IMers (my friends and pen pals aren't all that Internet savvy), but I'd try finding one to collaborate with if I were you.
I know your post is very old now but I`ll chip in with my little bit of knowledge about this particular traffic geo. I used to work with huge volumes of adult .jp traffic and one of the best converting niches was ebony based content.