Where are you seeing Japan as #1 in volume? Looking at
http://data.bitcoinity.org I'm seeing these volumes for the past couple weeks:
| Volume (in BTC) | Week 7/23 | Week 7/16 |
| USD/BTC | 621k | 982k |
| CNY/BTC | 180k | 255k |
| JPY/BTC | 94k | 168k |
Looks like Japan's volume is still way behind both China and the US.
Good information, china has always been the biggest rival for america and japan. In the future China will become a Super Power State, many predict as it is.
OP's post was from February when Japan was number 1 for a while in BTC. USD is however always king, whenever China, Japan or South Korea have shown up as number one in volume it has usually been based on data from exchanges with little or no fees which inflated the volume.