the princess with her father

Attila Kisbenedek/Agence France-Presse — Getty Images

On Sunday, Princess Mako, the eldest grandchild of Emperor Akihito of Japan, and Kei Komuro, her college boyfriend, are set to officially announce their engagement.

Law and tradition dictate that the princess, by marrying a commoner, will become a commoner herself. (Above, the princess with her father.)

Although this has happened before, the engagement has fanned a debate about whether the Imperial Household Law, which regulates Japan’s first family, needs changing.

To the Japanese public, the tradition appears increasingly anachronistic. Opinion polls find large majorities favor allowing women to remain in the imperial family after marriage, and allowing them to become sovereign.

After all, the wife of Akihito was a commoner before their marriage. Akihito’s successor, Crown Prince Naruhito, also married a commoner.

Even conservatives who oppose such changes see the threat of a potential succession crisis. The family now has only five men, including Akihito.

Japan has the oldest continuous monarchy in the world, but only eight women have ruled in the nearly 2,700-year history of the Chrysanthemum Throne.

People close to the emperor say that he agrees women should be allowed to succeed him.

“I don’t think he sticks to the narrow idea that only a male on the throne is acceptable,” a friend of the emperor recently told our correspondent.

Patrick Boehler contributed reporting.