The government has become so worried that it has dispatched envoys to several European countries, including Britain, to study a revolutionary possibility: that the law may be changed to allow a woman to ascend the Chrysanthemum Throne.
Compared with their British counterparts, Japan's royals are models of decorum, thrift and restraint. Cloistered behind the moat and thick walls of the Imperial Palace in Tokyo, they emerge publicly only a few times a year to attend national athletic meetings, plant trees, and wave at their subjects from behind bullet-proof glass.
Japan's compliant media have no truck with tabloid-style muck-raking, but the less reverent of the country's many weekly magazines have becoming increasingly preoccupied with the absence of imperial offspring.
Rumours about a future empress appeared to have been decisively quashed earlier this year by the newly-appointed Grand Steward of the Imperial Household Agency, Sadame Kamakura. "We are not thinking about the question of an empress," he said. "Our current system clearly specifies male succession to the throne, and it is working adequately."
But privately the agency, an obsessively cautious government organisation which controls every aspect of the Imperial Family, has been discreetly studying the possibility for several years. The problem has become increasingly worrisome with the continued failure of Emperor Akihito's children to produce sons.
Since their wedding in June 1993, Crown Prince Naruhito and Princess Masako have had no children. Next in line is the Emperor's younger son, 30-year old Prince Akishino, and both his children are girls. After him the succession would fall to a line of obscure and ageing uncles and cousins.
Since Prince Akishino, no male child has been born to any member of the Imperial Family.
Court officials have gathered written materials from Buckingham Palace and, in nine days' time, a senior official of the Imperial Household Agency will fly to Europe on a hastily arranged visit to the Netherlands, Belgium and Denmark. In Copenhagen, they will be briefed by court officials on the constitutional referendum in 1953 which allowed Queen Margrethe II to succeed after 600 years of Danish kings.
Any change would be complicated and controversial, requiring a parliamentary amendment to the Imperial Household Law and Constitution, which strictly regulate the duties, conduct and spending of the Emperor's family.
To a large extent, their low profile is a matter of cautious necessity. After the Second World War, Emperor Akihito's father, the late Hirohito, narrowly escaped being tried as a war criminal and the role of the Imperial institution arouses strong emotions in both nationalists and left-wingers. "Whether we recognise a female heir in the future depends very much on whether the Japanese people are ready to accept her or not," said an official of the Household Agency.
Women played a prominent part in Japan's early history. The founding deity, from whom the present Emperor claims descent, was the Sun Goddess, Amaterasu-no-Omikami.
The last Empress, Go-Sakuramachi, abdicated in 1770, and altogether seven out of Japan's 124 sovereigns have been women, although, like princesses throughout history, they have occasionally been the focus of scandals. In the eighth century, the Empress Shoken precipitated an alarming power struggle after an affair with a Rasputin-like monk.