http://www.interfax-religion.com/?act=news&div=8283
“”The number of the Japanese who identify themselves with Orthodoxy equals to about 30,000 people.
The Japanese Autonomous Church was founded by St. Nikolay (Kasatkin) who came to Japan on 1861 on the decision of the Holy Synod. He founded and headed the Russian Orthodox mission in Japan in 1870. He translated the Holy Scripture and liturgical books into Japanese and built the Resurrection Cathedral in Tokyo.””
30,000?
From my limited understanding of the religious landscape of Japan that is a pretty good sized denomination.