TOKYO (NYTIMES) - It looked a little lonely up there.

During the short, solemn ceremony on Wednesday (May 1) in which the new emperor of Japan, Naruhito, 59, accepted the sacred sword, jewels and seals that signify his right to sit on the throne, he was flanked by just two people. Standing ramrod straight to his right was his younger brother, Prince Akishino. To his left was his ageing uncle, Prince Hitachi, who sat in a wheelchair.

It was striking visual evidence of the imperial family's looming existential crisis: It has precious few heirs left.

Like Japan itself, the imperial family has a demographic problem. Just as Japan's population is shrinking and ageing, so is the royal family's. The line of succession, which is limited to men, is only three people long.

Besides the emperor's 53-year-old brother and 83-year-old uncle, there is only one other eligible heir: Prince Hisahito, the emperor's nephew. Because he is only 12, he was too young to attend Wednesday's ceremony. Under rules set by a government committee, only adult male members of the royal family are permitted to witness the rites.

"It's so obvious, right?" Mr Takeshi Hara, an expert on the imperial family and a professor at the Open University of Japan, said after watching the sacred regalia handoff on television. "The severity that the family faces is apparent."

Thirty minutes after the ascension ceremony, the women of the imperial family filed into the state room in the Imperial Palace, where the new emperor delivered a brief address before a group of politicians, judges, prefectural leaders and their spouses.

This time, Emperor Naruhito was flanked by 13 family members, 11 of whom were women.

Prime Minister Shinzo Abe has pushed a platform of elevating women in the often patriarchal Japanese workplace, hoping to supplement the country's dwindling labour force and energise its economy.

Similarly, the imperial family may have to consider permitting women to join the line of succession.

Under current law, women are not allowed to ascend to the throne, and women born into the royal family must renounce their imperial titles and officially leave the family once they marry. Their children - even males - cannot succeed to the throne.

When Japan's Parliament passed a one-time law in 2017 to allow Emperor Naruhito's father, Emperor Akihito, to abdicate, it attached an addendum that encouraged the government to study the possibility of allowing women born into the royal family to remain within the imperial household after marrying.

Such a move would expand the pool of available heirs if the women were granted the right to head legitimate lines of succession, even if they could not sit on the throne themselves.

On Wednesday, Mr Abe's chief Cabinet secretary Yoshihide Suga said in a news conference that the declining number of imperial heirs was "an extremely important issue related to the fundamentals of the state".

He said the government would conduct discussions about allowing royal women to remain within the imperial family "deliberately and carefully".

Emperor Naruhito and his wife, Empress Masako, have just one child, a daughter, Princess Aiko, 17. After she was born, the government briefly considered changing the law to allow women to join the line of succession. But once Prince Hisahito was born, such discussions were shelved.

Conservatives oppose proposals to admit women to the line of succession, citing tradition and notions of pure-blood legitimacy.

If women were allowed as emperors, said Professor Hidetsugu Yagi, a law and philosophy expert at Reitaku University in Chiba Prefecture, "the imperial family would be no different than any other ordinary family".

"Eventually," he said, "the imperial system would end."

In fact, rules barring women from heading lines of succession date back only to the 19th century, in the Meiji era. And over the 126 generations of recorded emperors in Japan, eight women ruled when no adult men were eligible at the time.

The emperor and other members of the imperial family are extremely circumspect in their public comments, so it is impossible to know for sure what they think about the succession problem.

Earlier this year, Emperor Naruhito acknowledged that there were few remaining heirs and specifically referred to "the declining ratio of male imperial members". But even if he wanted to, it would be difficult for the new emperor to change the rules.

"It's not as if we can expect him to take radical action," said Ms Kristi Govella, an assistant professor of Asian studies at the University of Hawaii, Manoa. "There are many actors who would be involved, particularly in actually changing the rules of succession." Any changes to imperial law must be approved by Parliament.

Still, those who resist change may have to yield to reality, said Mr Kenneth Ruoff, a historian and specialist in Imperial Japan at Portland State University. "Everybody in Japan now speaks openly about the fact that the future of the imperial line is in grave danger," he said. "They don't have any choice but to revisit the issue."

Outside the Imperial Palace, following the ascension rites on Wednesday, well-wishers gathered in hopes of getting a glimpse of the new emperor, with some saying they wished that the imperial family could change how it treats women.

"What's wrong with a female emperor, I wonder?" said Ms Yukiko Minegishi, 41, who works at a uniform maker in Tokyo and had come to the palace with her mother.

She added that the prohibition against women in the line of succession was, like other gender-related traditions in Japan, out of step with the times.

Ms Minegishi noted that women are not allowed in sumo rings, another practice that has come under scrutiny, after a referee last year shooed women out of a ring when they rushed to offer lifesaving measures to a politician who had collapsed while delivering a speech.

"Those practices need to change in the modern era," Ms Minegishi said. "Men and women should be treated equally."

Although any overhaul of imperial rules may take time, some analysts wondered if the new empress might subtly serve as a role model for women in society.

A former diplomat, Empress Masako could be enlisted as a cultural ambassador for Japan. Shortly after her marriage, she impressed observers when she sat between then President Bill Clinton and Russian leader Boris Yeltsin at a state dinner and conversed easily with both of them in their own languages.

She could soon have the opportunity to flex her diplomatic skills: United States President Donald Trump will be the first foreign leader to meet the new emperor and empress when he arrives in Tokyo later this month.