Japan is on standby for the birth of an heir who will ensure the future of the imperial f amily - if it's a boy, writes David McNeill

For the next 24 hours, the eyes of much of Japan will be trained on a single room in a private hospital in the centre of Tokyo, where a 39-year-old woman is waiting to deliver her baby by Caesarean section. When the baby utters its first scream, TV programmes will be interrupted, politicians will make speeches and the major newspapers will distribute millions of special supplements: four pages for a boy, two for a girl.

But then, this is no ordinary toddler but one born into controversy and with the weight of the world's oldest hereditary institution on its tiny shoulders. If it is a boy, he will one day head a dynasty that claims to trace its roots back to before the Romans stepped on British soil. If it is a girl, she will come into the world to the sound of a huge collective sigh of disappointment. Not an easy start in life.

Such are the sexual politics of what may be Japan's first male imperial birth since 1965. Officially, the government, as its chief cabinet spokesman Shinzo Abe said last week, hopes Princess Kiko gives birth to a healthy baby of either sex tomorrow; unofficially it is praying that the baby will have a Y chromosome and rescue the Imperial Family from a succession crisis that could make it extinct within a couple of generations.

Everyone knows that this is a soufflé that cannot rise twice. At almost 40, and after a complicated pregnancy that put her in Aiiku Hospital on August 15th to prevent possible premature bleeding, Princess Kiko will almost certainly never have another child. Her sister-in-law Masako, 43 this year, has been so worn down by her transition from diplomat to member of the cloistered Imperial Household that rumours of depression, divorce and worse abound.

They are the wives of Emperor Akihito's two sons - Prince Naruhito and his younger brother Akishino - and these two couples are the family's last hope for a male heir. The once sprawling imperial family tree, and its system of concubines as hired wombs, has been pruned by postwar reforms to a tiny nub.

This, in other words, is a dynasty fighting for survival. Without radical legal change "the Imperial Family will end with the deaths of Crown Prince Naruhito and Prince Akishino," says Japan historian William Wetherall.

In a world struggling to deal with the melting Polar ice caps and the disintegration of the Middle East, the problems of Tokyo's Imperial Household might seem like very small fry. But traditionalists believe the family boasts an unbroken bloodline that stretches back over 125 generations and 2,000 years and which has survived war, revolution and Japan's transition to a modern secular democracy. Some even cling to the myth that Emperor Akihito is a direct descendent of the sun goddess Amaterasu, and "the father" of the "pure" Japanese race.

Such ideas of racial purity have officially been banished from political thought in the gleaming modern country that Japan has become since the second World War. But they still lurk around its conservative fringes, as Prime Minister Junichiro Koizumi discovered earlier this year when he tried to change the male-only succession law and allow Princess Masako's daughter, four-year-old Aiko, to eventually warm the Chrysanthemum Throne.

Although public support for the move was at one point over 80 percent, conservatives, many in Mr Koizumi's own Liberal Democratic Party, fought the revision hard. LDP bigwig Hiroyuki Hosada warned that the succession issue could "split the country" if handled badly and 170 Diet (parliament) members signed a cross-party petition opposing the legislation.

The government's former trade minister, Takeo Hiranuma, warned a panel of law-makers opposed to the revision that "if Aiko becomes the reigning empress, and gets involved with a blue-eyed foreigner while studying abroad and marries him, their child may be the emperor." He added: "We should never let that happen." The emperor's cousin, Prince Tomohito, even recommended reinstating the tradition of concubines.

ALTHOUGH ALL EYES are on Kiko, it is her enigmatic sister-in-law Masako who has sparked this crisis. Drawn across the imperial moat by a mixture of love and duty, the multilingual career diplomat symbolised the growing freedoms of Japanese women and many hoped she might help modernise one of Japan's most conservative institutions. Instead, she became, in the words of one commentator, a "prisoner of her womb", expected to produce a male heir [though of course it is through the father that a baby's sex is determined] and abandon her ambitions for imperial diplomacy.

In 2001, after over seven years of marriage she finally had a girl, Aiko, bitterly disappointing conservatives. The birth, following IV treatment, was traumatic, as was adjustment to life with the bureaucrats who run the Imperial House Agency (IHA), but worse was to follow. In 2003, the Imperial Household Agency's Grand Steward, Yuasa Toshio, lapsed into the language of the stud farm when he said that he "strongly wanted" the now middle-aged couple to have another child. The princess withdrew from official duties that December and has never returned to a full roster.

She is currently on holiday in The Netherlands with her husband, daughter - and the family psychiatrist. Officially, Masako suffers from an "adjustment disorder", a stress-induced condition normally associated with people struggling to readjust to a new life. But like many observers, Ben Hills, who has spent a year researching a book on Masako, says she is "chronically depressed" and unhappy with life in her gilded cage.

"She is being treated with drugs and cognitive therapy under the supervision of a doctor who wrote a book about preventing suicide among elderly people," says Hills. "She is still a sick woman. Who else goes on holiday and takes along their own psychiatrist?"

Many conservatives now intensely dislike the princess and there has been a notable rise in Masako-bashing online, where bloggers describe her as a show-pony and a moaner who is too haughty for the "humble, mandatory work" of imperial life. Although the mainstream Japanese media shies away from such blunt commentary, some pundits have stuck their heads above the barricades to suggest the imperial "quagmire" might be resolved if Naruhito divorced Masako and remarried.

"Her withdrawal from the imperial family would certainly solve a lot of problems," commentator Yagi Hidetsugu, told a weekly magazine recently.

Masako's options may narrow if, as many predict, Kiko delivers a boy tomorrow; a Tokyo magazine said this week that the baby's father, Prince Akishino, let it slip to a friend that after two daughters, his next child will be a son. That might take the pressure off Masako, or it could be the final straw for the beleaguered princess.

"It looked as though Masako's daughter would be the first reigning empress in modern Japanese history and Masako would have been the one who shaped her. And now she doesn't even get to do that," says Ken Ruoff, author of The People's Emperor. "So she may well ask herself: what is the purpose of all this? Why have I made all these sacrifices? People who know say this is a really dicey situation and that she is really unhappy."

Ben Hills says there are other ways for her to escape. "One-third of people suffering from chronic depression take their own lives; that's a sad fact. Or Prince Naruhito could renounce his claim to the throne for the sake of his wife's health and hand it to his brother. The likelihood is very low because he is a dutiful man, but on the other hand he is deeply in love with Masako and must hate to see her suffering. There are no easy options."

All will become clear sometime in the next few days when the baby at the centre of this drama wails into life. One publication estimates that a male infant will bring a boost the economy to the tune of more than US$ 200 million; the editors didn't bother to calculate the economic dividend from a girl.

But some are thinking the unthinkable: what if the latest addition to this troubled family is born without testicles? The question was put - not quite in that way, of course - to Mr Abe, who said the government should be "cautious" in discussing any revision to the 1947 Imperial Household Law.

"The succession is connected to the very basis of our nation, so we consider it a very serious issue," said the man most likely to replace Mr Koizumi as Prime Minister next month. Like Mr Koizumi, he does not relish another fight with members of his own party, or the powerful Association of Shinto Shrines, which has traditionally harvested votes for the LDP in local districts.

NOT EVERYONE WILL be unhappy with a girl. Feminists believe this would force the government to face down the old guard and provide a powerful symbolic boost to Japanese womanhood. "It would be very important if the national symbol could be a woman, and in fact it is ridiculous that it isn't," says Ken Ruoff. "An empress would also make it difficult for the patriarchal far right to hold onto their chauvinism."

Others say the fuss over the sex of the baby misses the point. "The main problem is the lack of access to the family, and the secrecy that surrounds it," says journalist Tomoko Ugajin. "The imperial family remains incomprehensible to most Japanese."

That secrecy means that when the fuss has died down, the new baby will be whisked away behind the high walls of the Imperial Palace, to be wheeled out on official photo opportunities. The child's life will move in tandem with the ancient rhythms of tradition, overseen by the same IHA bureaucrats who have made life miserable for its aunt.

Even with a male birth, this is a family that may not be around to see the next century. Unless the law changes, Aiko and her two first cousins, Mako and Kako (Princess Kiko's daughters) will marry commoners and disappear into civilian life, provided they can persuade suitors to endure the painful scrutiny that comes with dating a princess. That leaves just one boy to carry the entire imperial load, and whatever woman he can rope into life behind the palace walls.

"That's one nuclear family to bear the entire weight of the Chrysanthemum Thorn - still surrounded by a legal moat called the Imperial Household Law, and a bureaucratic one called the Imperial Household Agency," says Wetherall. The little imperial bundle of joy has no idea what is in store for him - or her.

'Only his majesty walks in the centre' Inside the Imperial Palace

Most foreign journalists get at least one opportunity to step inside Tokyo's Imperial Palace and it is always an interesting experience. I visited the palace to cover Taoiseach Bertie Ahern's visit to Japan.

On a sunny morning, I arrived with a small party of photographers and journalists inside the Palace ground, set in 300 sprawling acres of greenery in the heart of Tokyo. We were met by an Imperial Household Agency official, a superbly unpleasant and sniffy bureaucrat, who did not feel the need to smile or even greet us in the usual formal Japanese way. He immediately raised a fuss over the dress code of an RTÉ cameraman, sparking a mad scramble for a jacket before our 11am deadline to meet the Emperor.

On the way to the Emperor's official meeting room for foreign dignitaries, the official complained that it was "rude" to turn up in informal clothes to meet "his majesty". He then berated me for walking in the centre of the long hallway leading to the room. "Only his majesty walks in the centre," he said, banishing me to the edges of the carpet. In the meeting room, we were told we would have 90 seconds to photograph the Emperor as he arrived to greet the Taoiseach. We should be careful not to make any noises when he entered the room. We would leave directly afterward.

Princess Masako and the dwindling band of royals are surrounded by people like our handler, with their total dedication to the emperor cult and the countless arcane rules that structure it. The handlers rigidly control all aspects of imperial life and media access. When Princess Kiko married Prince Akishino, a photographer who snapped the new bride brushing hair out of her husband's eyes before a formal portrait was banned for life.

One former Imperial House correspondent says he was once told off by bureaucrats for asking the emperor if he had recovered from a cold. "That's how much they control things," says the journalist. As the Imperial correspondent for Japan's top news agency said, "Now you know why Princess Masako has become ill. There are so many old rules like these that must be making life unbearable for someone who was used to having a lot of freedom. I feel very sorry for her."