Recent survey done by Japan.Internet.com shows that 70% of Japanese use 2 or more search engines. Yahoo Japan was the most popular search engine, and Google was the close second.

Not getting good search results was the top reason for using multiple search engines. About 25% said that what they want to search makes difference in which engines to use. Instead of looking at the page 2, they go to next search engine to search the same keyword phrase. (People looking for shopping and entertainment related information tend to use Yahoo, maybe? I know that B to B businesses usually do better with Google Japan.)

This results mean that if you are targeting Japan market, you need to do well (both SEO and PPC) with both Yahoo Japan and Google Japan, and not just one of them. It also shows that people are reading the search results closely instead of clicking what comes up at #1 or #2 automatically. Check your page description in search results for your target keywords to make sure it has a good description of the page.