A while back Age of Empires III: The Asian Dynasties was announced as the second expansion to Age of Empires III. The expansion will, as the title explains, focus on Asian dynasties. These civilizations include Japan, China and India. Recently Game Trailers has posted a video discussing the Japaneses civilization. If you have Flash, you can see the Video Below.
You might also be interesting in reading the Japanese Q&A from Gamespot.