The new Japanese constitution after world warll contained a clause that

The constitution provides for a parliamentary system of government and guarantees certain fundamental rights. Under its terms the Emperor of Japan is "the symbol of the State and of the unity of the people" and exercises a purely ceremonial role without the possession of sovereignty.

The constitution, also known as the "Post-war Constitution" (戦後憲法, Sengo-Kenpō?) or the "Peace Constitution" (平和憲法, Heiwa-Kenpō?), is best known for its Article 9, by which Japan renounces its right to wage war; and to a lesser extent, the provision for de jure popular sovereignty in conjunction with the monarchy.

The constitution was drawn up under the Allied occupation that followed World War II and was intended to replace Japan's previous militaristic and system of quasi-absolute monarchy with a form of liberal democracy. No amendment has been made to it since its adoption. [1]