The Constitution of Japan defines the emperor[1] to be "the symbol of the state and of the unity of the people." He performs ceremonial duties and holds no real power, not even emergency reserve powers. Political power is held mainly by the Prime Minister and other elected members of the Diet. The Imperial Throne is succeeded by a member of the Imperial House of Japan as designated by the law.
The chief of the executive branch, the Prime Minister, is appointed by the Emperor as directed by the Diet. He must be a member of either house of the Diet and a civilian. The Cabinet members are nominated by the Prime Minister, and they must also be civilian. Since the Liberal Democratic Party (the LDP) was in power, it has been convention that the President of the party serves as the prime minister.
The Cabinet is composed of Prime Minister and ministers of state, and is responsible to the Diet. The Prime Minister has the power to appoint and remove the ministers, a majority of whom must be the Diet members. The liberal conservative LDP was in power from 1955 to 2009, except for a very short-lived coalition government formed from the likeminded opposition parties in 1993; the largest opposition party was the social liberal Democratic Party of Japan in the late 1990s