How did the role of the Japanese Emporer differ from the role of the Chinese emperor?

The criterion here is the real power the emperor in China and Japan had. The Chinese emperors exercised absolute power, they were the center of the Chinese imperial political system. They had real power. On the contrary, the Japanese emperors played mainly a symbolic role through most of Japan's history; for many centuries, the real power was in the hands of local feudal lords, although the emperor was seen as a divine being, a living god. In the Tokugawa period, the emperor continued to play that symbolic role, but the shogun - the head of the army - enjoyed effective political and military power.

There is one interesting difference between the two: In China there are many dynasties, and therefore many families of emperors. Most Chinese dynasties ends within 300 years of its foundation. However, in Japan, all 125 emperors spanning millennia are said to from the one same family.