With Wednesday's ascension of new Emperor Naruhito following his father's abdication, questions have risen about roles to be played by women in the royal family amid concerns over future imperial successions and how to shoulder public duties in an ever-shrinking imperial household.
Under the 1947 Imperial House Law, only males with patrilineal lineage can ascend the throne. Women who marry commoners must leave the imperial family.
Of the current 18 imperial family members including former Emperor Akihito, 85, and former Empress Michiko, 84, who no longer perform official duties, 13 are women.
At present, there are only three heirs to the throne -- Emperor Naruhito's younger brother Crown Prince Fumihito, 53, his son Prince Hisahito, 12, and the emperor's uncle Prince Hitachi, 83.
[Photo courtesy of the Imperial Household Agency]
Princess Mako, 27, the elder daughter of the crown prince, may abandon her royal status in the near future upon marriage to Kei Komuro, 27, her boyfriend from university days.
Princess Aiko, the 17-year-old only child of the emperor, would be entitled to the throne in a British or Dutch monarchy that adopts the rule of successions by the eldest child regardless of gender, but she is barred from succeeding her father under the current Japanese law.
Experts are sounding the alarm that the imperial line may disappear completely if the Imperial House Law is not revised. Concerns also exist that should women marry out of the household, the burden of official duties will fall onto a smaller number of family members.
With Emperor Naruhito, 59, and Empress Masako, 55, taking on the duties previously held by former Emperor Akihito and former Empress Michiko, the new imperial couple's key functions will be handed down to Crown Prince Fumihito, who will retain part of his previous duties, and 52-year-old Crown Princess Kiko.
Some duties formerly performed by the crown prince and crown princess will be passed to Princess Mako. After she leaves the imperial family upon marriage, her younger sister Princess Kako, 24, is expected to perform them.
To address the situation, some experts suggest either reducing the number of public duties or increasing the number of those who can do them by allowing female imperial family members to retain their royal status even after marriage to commoners.
The Japanese government has periodically considered revising the Imperial House Law to allow female succession or the establishment of women members' own branches by letting them stay in the household even after marriage to lighten the load of public duties on each individual.
In 2005, an expert panel called for a law revision to allow the imperial couple's first born regardless of gender to ascend the throne, and recognize matrilineal succession. But the impetus was halted with Prince Hisahito born in 2006 as the first new male member of the royal family in nearly 41 years.
Debate on the launch of female branches has also been stymied by opposition from conservatives, who represent the core support base of Prime Minister Shinzo Abe and claim it could pave the way for women members to succeed to the throne or those with female lineage to do so.
Of all 126 emperors so far, including the legendary first emperor, Jimmu, eight women who were all born to the male lineage of the imperial family ascended the throne.
A one-off law enacted in 2017 to allow former Emperor Akihiro's abdication adopted a nonbinding resolution for the government to consider measures ensuring stable imperial successions without a deadline.
In March, Chief Cabinet Secretary Yoshihide Suga said the government will start a study on whether to allow female members to remain in the imperial family even after marrying commoners immediately after Emperor Naruhito ascends the throne.
But Abe is seen as negative to an early start of discussions to ensure stable imperial successions, as he has in the past called for the return of distant blood relatives -- members of 11 collateral branches that left the imperial family in 1947.
The prime minister and his supporters believe that the hereditary monarchy, which is said to stretch back more than 2,600 years with the throne consistently passed down the male line, should continue the same way.
"The principle behind imperial successions up to the current 126th monarch is that they were all of the male bloodline," argues Hidetsugu Yagi, a professor of constitutional law at Reitaku University.
"Historically speaking, the succession principle based only on male lineage has firmly established the status of emperors. Will a future emperor with female lineage be considered legitimate? We should not confuse imperial succession with modern society's trend toward gender equality and women's empowerment," he said.
Itsuo Sonobe, a former Supreme Court justice who was an acting head of the expert panel in 2005, said he is against such an idea. "Without accepting women emperors or female branches, Japan could face the crisis of the imperial household's demise."
"Globally speaking, there are queens and female prime ministers. But Japan is still a male-centered society and it is discouraging," he said.
In a Kyodo News poll conducted last December, 84 percent said they support women emperors and 76 percent were favorable toward establishing female branches.
Female royal family members can play powerful roles by attracting public interest through their exposure to the media and help keep the imperial household relevant in a modern society, points out Ayuu Ishida, a professor of media culture at Momoyama Gakuin University.
Many younger-generation female imperial family members engage in duties by making the most of their international, educational or professional experiences. At present, there are six unmarried women up to in their 30s in the imperial household.
(Princess Mako visiting Bhutan in June 2017)
(Princess Mako gives an address in sign language in August 2017)
(Then-Princess Ayako and her mother, Princess Hisako, observe a Sea Cadet training session in September 2018)
In a first for female members who married commoners, Ayako Moriya, 28, the youngest daughter of Emperor Akihito's late cousin, retains honorary titles at two organizations even after leaving the imperial family upon marriage last October.
Some think she could be a model for women who continue to retain previous functions regardless of marital status.
Empress Masako, a Harvard- and Oxford-educated former diplomat suffering from a stress-induced illness for a long time, may also change people's expectations about how duties should be performed by the imperial couple, as she would continue to limit her public appearances due to her conditions.
Unlike former Emperor Akihito and former Empress Michiko, who usually engaged with the public as a couple, Emperor Naruhito will perform public functions on his own as his wife suffers from adjustment disorder, but the general public will soon get used to it, said Masahiro Yamada, a professor of sociology at Chuo University.
"Modern society attaches importance to work-life balance, and if the imperial household is keeping up with the times, that is also necessary for both the emperor and the imperial family," he said. "The emperor and empress should each do what they can do."