The decision last Friday by the Imperial Household Council, chaired by Prime Minister Shinzo Abe, finally sets the stage for Emperor Akihito to retire on April 30, 2019, in the first Imperial abdication in about 200 years — and the first in the Imperial system under the postwar Constitution. Special legislation was enacted in June, applicable solely to the current aging Emperor in response to his wish indicated in a video message last year to step down — which is not provided for in the Imperial House Law's succession rules. Discussions on Imperial abdication have shed light on questions surrounding future succession in the Imperial family — an issue that should also be promptly addressed.

The one-off legislation enables 83-year-old Emperor Akihito to abdicate without amending the Imperial House Law, which stipulates that an emperor is to be succeeded by the heir upon his death. The law also says that only male members of the Imperial family on the paternal lineage can be heirs to the throne. When Crown Prince Naruhito, the Emperor's eldest son, ascends to the throne the day after the abdication, his brother Prince Akishino will be the second in line. Currently, Prince Akishino's 11-year-old son, Prince Hisahito, is the sole male member of the family younger than his father.

Under the law, female members of the Imperial family lose their royal status when they marry outside the Imperial family. Prince Akishino's eldest daughter, Princess Mako, is scheduled to marry her former university classmate next November. Of the current 18 Imperial family members supporting the Emperor, 14 are women. When Princess Mako leaves the Imperial family, there will be six women up to their 30s, including Crown Prince Naruhito's 16-year-old daughter, Princess Aiko. If they also marry and leave the Imperial family in coming years, the Imperial family could be further depleted.