if you can/know how to use torrents, i recommend
http://extratorrent.com/view/popular/Adult+-+Porn.html
you can just type in 'jav', 'censored', 'uncensored', 'tokyo hot', 'catwalk poison'... etc... and all the jap porn will be available. browse thru the screenshots. if you see what you like, download.
or else try xhamster for streaming purposes.