Imperial Household Law applies to jurisdiction Japan
The Imperial Household Law of 1947 (皇室典範, Kōshitsu Tenpan) is a Japanese law that governs the line of imperial succession, the membership of the imperial family, and several other matters pertaining to the administration of the Imperial Household.  
In 2017, the National Diet changed the law to enable the Emperor to abdicate within three years. With this change, Emperor Akihito abdicated on 30 April 2019.