The site matches users based on an algorithm of 29 dimensions.
To find them, you can choose "Japanese" as the ethnicity at the search function.
International Cupid Popularity: International Cupid is an international dating site with some Japanese members.
Friend Finder Popularity: The international dating site attracts a small number of Japanese single members.
Popularity: actually has a very popular Japanese sister site, jp.match.com, with huge number of Japanese members.
Unfortunately, jp.is in Japanese, so it's difficult for you to use the site, unless you know Japanese well.