IJapan.org is a web proxy located in Nagano, Japan. The IP of the server is 121.50.43.189.
From the proxy description:
Nowadays, many ads are geotargeted such as Google’s Adwords/Adsense, Yahoo’s Search Marketing/Publisher Network or other PPC (Pay Per Click) engines. If you want to see exactly the same banners as a Japanese visitor sees, please uncheck “Remove client-side scripting [...]