Actually, Japan has charged for years that China "exports deflation" by underselling other manufacturing nations. According Haruhiko Kuroda and Masahiro Kawai argued in the Financial Times "China is exporting deflation, it is spreading through export growth and a combination of domestic price inflation and an exchange rate pegged to the dollar." However, this saying is unreasonable, because the import amount from China just occupy 2% of GDP of Japan. Furthermore, most of those products are low value. That means Chinese products can not impact Japanese price level, therefore appreciation of Renminbi will not benefit Japanese economy. .
In addition, appreciation of Renminbi will cause damage to interests of Japanese corporations. Over the past decade, much of the world's manufacturing had moved to China for cheap labor and resources, include Japanese enterprises. A great deal of Japanese corporations set their manufacture bases in China instead of Japan for lower cost. So, if the appreciation of Renminbi comes true, those Japanese enterprises will suffer from it. .
Last, Japan considered that appreciation of Renminbi will be a good way to save their economy and restrain the growth of China, the future competitor. However, Chinese advantages will not be weaken simply by higher value of its currency, because the stronggest advantage of China is the infinite cheap labors but not cheap currency. The level of Chinese salary is much more cheaper than its competitors, such as Japan, Malaysia, Singapore, and Taiwan. Therefore, even if China appreciate Renminbi, Chinese exporter will recapture the market share by reducing salary of workers.
The United States.
The only super country is suffering from economic depression, although the government have tried several ways to stimulate economy. There are two main possible reasons for United States support the claim of reveluate Renminbi, economy and politics.