Japan's been ruled by the same family since 660 BC!
The Imperial Family, officially known as the Imperial House of Japan, is the extended family of the reigning Emperor of Japan. They take on the official and public duties of the government. Other family members of the Emperor perform social and civil duties unrelated to the governmental affairs. The duties of the Emperor are passed down to his children and their children and so on.
The Japanese monarchy is the oldest continuous hereditary monarchy in the world. The current Japanese monarchy began with the legendary Emperor Jimmu in 660 BC. Since then there have been 124 recognized monarchs, including the current reigning emperor. However, there isn’t any actual genealogical evidence of relationships or even the existence evident of the first 25 emperors.
The current emperor is Emperor Akihito who has reigned since 1989. The succeeding emperor is based on birth order of boys. Akihito was the eldest of 5 boys and succeeded his father, Hirohito.