Japanese Imperial family had been around for milleniums, but Chinese Imperial family changed each time the dynasty had changed.
Why? While Chinese emperor was like a 'King' who ruled the country by power, Japanese emperor was more like the 'pope' who have had power at one stage but later turned into nothing but a subject of religious belief.
In China, the country had 13 different dynasties over 4 milleniums up until early 20th century when the 'Last Emperor' resigned. Each Imeprial family was extincted when a new one arose. The country was basically ruled by the Emperors throughout the history with exceptions of the periods of civil wars.
In Japan, the Imperial family was only in charge of the country before 11th century, and the small period after the Meiji Restoration and before WWII ended.
