The imperial family of Japan has yet to give the country's hungry tabloid media any toe-sucking sexual exploits, or toe-curling pledges of love - and, given the largely uncharismatic individuals in question, one hopes it never will. The raciest thing recently was last year's front-page photo-shocker of Emperor Akihito's and Empress Michiko's jerky rendition of "I'm a Little Teapot" before a class of primary schoolchildren. Before that was the 1960 headline "Your Imperial Highness, your trousers are too large", above an article which ruled that the trews sported by the then crown prince were wider than fashion required. The far right was still complaining about that a decade later.
It's not that in the 20th century Japan's monarchy was brought low, relatively speaking, but rather that it fell from so high. The trajectory of its descent is traced by Kenneth Ruoff in his detailed (if dutiful) new study, The People's Emperor. Japan's royal house entered the last century as the "Imperial Throne coeval with heaven and earth" (1890 Imperial Rescript on Education); postwar, it plummeted to being a mere "symbol of the state", as stipulated in the 1946 constitution drawn up by the occupation forces; and it crashed to earth in the modern era as the "emperor system of the weeklies", derided by Yukio Mishima, the brilliant author who, in 1970, ritually disembowelled himself in the name of the emperor.
As this history shows - and as vocal nationalists have always maintained - Japan is a special case, moulded by an occupation-imposed constitution. At the same time, it offers laboratory conditions in which to observe the evolution (or devolution) of the monarchic principle in an age of ascendant democracy. Britain is the ever-present "control" for Japan's polity experiment - both as role model and, more recently, as cautionary tale. Not that Britain's royal house was always one step ahead in the egalitarian stakes; the Queen's 1953 coronation, with its retinue from the colonies and protectorates, was the last gasp of imperial ceremonial, and as late as 1963 royal preference was decisive in the selection of Alec Douglas-Home to succeed Harold Macmillan as prime minister.
Ruoff is a clear-eyed observer of the post-occupation battle for Japan's soul that pitted left against right over issues such as constitutional revision, the reign-names system and the authenticity of the national foundation myth. In doing so, he breaks down the all-too-prevalent tendency to view Japanese politics, of the immediate postwar and present, as monolithic and staunchly conservative.
Certain hot-button issues forced ideological opposites to make common cause. In the 1990s, the far right and the Japanese Communist Party agreed that the emperor should not offer apologies for Japan's wartime treatment of its Asian neighbours, the former because it believed that no apology was necessary, the latter because of its insistence on the emperor's constitutional status as a "symbol" - and thus as an individual not qualified to make statements on behalf of the nation. Such doublethink was present, too, in the minds of politicians such as Yasuhiro Nakasone, perhaps Japan's most influential postwar lawmaker. A lifelong conservative and nationalist, he none the less proudly affirmed Japan's ties to the United States, and in 1983 pledged that the country would be "an unsinkable aircraft carrier" at the disposal of its ally.
The emperor's role, as Nakasone saw it, was that of the apolitical man of peace, culture and scholarship - and this ideal has in many ways been realised in Akihito and his mild-mannered, studious children. The imperial family retains an aloof and anachronistic dignity of which members of the British royal family can only dream. The Inspector of the Imperial Stools (bowel movements, not three-legged furniture) was dismissed only in 1989, and the emperor's image never appears on stamps, even for commemorative occasions, for fear that postmarks might deface it.
And yet the yawn of indifference that greeted the arrival of Princess Aiko, the only child of Crown Prince Naru-hito and Princess Masako, suggests that dignity goes only so far in winning the popularity ratings game. The Imperial Household Agency - often painted, like its fellow conservative organisations, as an immovable, united front - pays obsessive attention to opinion polls, and its presentation of the monarchy is more responsive and less prescriptive than is generally understood.
It was Prince Philip who remarked that a modern monarchy wages a permanent charm offensive, "fighting an election every day of the week". Utterances of the household agency are usually more gnomic, but one palace official, in 1998, told the American journalist Gale Eisenstodt: "Emperor Akihito realises that the greatest challenge for a monarchy in a democratic society is simply to survive."
Despite differences historical, cultural and behavioural, Britain's royal family and Japan's imperial house will surely one day find themselves playing the same slow republican endgame.
Victoria James is the New Statesman's Tokyo correspondent