I am going to index wikis belonging to category:Japan or category:Japanese which use MediaWiki.
I may exclude wikis that are more or less private home page rather than community home page, such as wiki with only one registered user.
User:Nightingale/work in progress
- Free wiki hosting
list: Category:Wiki farm
Wikia, Wikispaces, @wiki, Seesaa Wiki (previously known as Livedoor Wiki), CentralDesktop, WikiHouse