Regency is established in accordance with the Imperial House Law (Constitution of Japan, Article 5).
When the Emperor is a minor, Regency is established. In case the Emperor is afflicted with a serious disease, mental or physical, or there is a serious hindrance, and he is unable to perform his acts in matters of State, Regency is instituted by a decision of the Imperial House Council (Imperial House Law, Article 16).
The Regency is assumed by a member of the Imperial Family, who is of age, according to the following order (Imperial House Law, Article 17).
The Regent performs acts in matters of State in the Emperor's name, The Regent performs only such acts in matters of state as are provided for in the Constitution and does not have powers related to government. (Constitution, Article 5).
The Regent, while in office, is not subject to legal action. However, the right to take the action is not impaired hereby (Imperial House Law, Article 21).