The Constitution of Japan is adopted through Emperor's assent.

The Constitution of Japan is the supreme law of Japan. Written primarily by American civilian officials during the occupation of Japan after World War II, it was adopted on 3 November 1946 and came into effect on 3 May 1947, succeeding the Meiji Constitution of 1889. The constitution consists of a preamble and 103 articles grouped into 11 chapters. It is based on the principles of popular sovereignty, with the Emperor of Japan as the symbol of the state; pacifism and the renunciation of war; and individual rights.

Royal assent is the method by which a monarch formally approves an act of the legislature, either directly or through an official acting on the monarch's behalf. In some jurisdictions, royal assent is equivalent to promulgation, while in others that is a separate step. Under a modern constitutional monarchy, royal assent is considered little more than a formality. Even in nations such as the United Kingdom, Norway, the Netherlands, Liechtenstein and Monaco which still, in theory, permit their monarch to withhold assent to laws, the monarch almost never does so, except in a dire political emergency or on advice of government. While the power to veto by withholding royal assent was once exercised often by European monarchs, such an occurrence has been very rare since the eighteenth century.