SEO in Japan is pretty much the same as it is here and every other country. The only difference is which is the preferred search engine used in each country.
Below is a map of the world corresponding to preferred search engine (click image to enlarge):
As you can see, Yahoo! is the preferred search engine in Japan so it is best to build a site that meets Yahoo! search engine standards if one wants to succeed in organic online marketing geared towards Japanese search engine users.
And where does Microsoft’s search engine “Bing” fit in to all of this?
The answer might surpise you…
Yahoo! signed an agreement with Microsoft in 2009 so that Microsoft’s search engine( Bing) will provide Yahoo’s search results behind the scene. As of now, all of Yahoo! Search global customers and partners have been transitioned to Bing.
So if you really want to rank a website in Japan then focus on Bing’s algorithm. Since Yahoo! relies on Bing technology (and identical search results prove that) if you can build a site around Bing’s algorithm “demands” then you can rank a site in Japan for any keyword you want.