The world's oldest unbroken monarchy has one problem no ceremony can solve: the heir may not inherit. Aiko, the only daughter of Japan's Emperor Naruhito and Empress Masako, stood on Sunday at the centre of one of the country's holiest rituals, dressed in white from head to toe, pearls at the collarbone, gloves on - and even as she did it, the law keeping her away from the Chrysanthemum Throne continues to be written without her.

The journey ran from the Imperial Palace in Tokyo to Ise, in Mie prefecture, home to Shinto's holiest complex. The reason is the reconstruction of the Grand Shrines at Ise - a custom repeated every twenty years and running unbroken for 1,300 years. The next great renewal begins in 2033. The preparations, then, begin now, and they begin with her.

This is not a photoshoot. Ise houses the Sacred Mirror, one of Japan's three sacred treasures, symbolising wisdom and, by legend, used to draw the sun goddess Amaterasu out of a cave. The other two are the Kusanagi sword, for courage, and the Yasakani no Magatama jewel, tied to benevolence and to the legitimacy of the Imperial House. The Inner and Outer Shrines date back some 2,000 years. When a state transmits authority through objects of that age, anyone standing beside them receives something no election can confer.

And there is the irony. Aiko bowed to Amaterasu - a goddess - and then attended Kawabiki, the traditional hauling of logs along the river, taking hold of the rope alongside hundreds of ordinary citizens. Before that, in town, she boarded an ordinary metro train among the crowd. A scene any court adviser would call symbolism of closeness to the people. Except symbolism does not amend an article of law.

The clothing was ivory white, light fabrics, restrained cut - and, as protocol notes, exactly what she had already worn at a previous official appearance. White in Japan means purity and renewal, in the spirit of Shikinen Sengu, the rite of periodically returning the shrines to their original state. Pearls are the "official" jewellery of court ladies because they display elegance without displaying wealth. Not one item is accidental, and not one is her choice.

So this is the picture: a woman who publicly represents the oldest dynasty on the planet, whom the public adores, who knows every ritual by heart - and who, under the current Imperial House Law, cannot take the throne, and who loses her title outright if she marries a man from outside the imperial family. Reform of that law has been discussed for years and keeps being postponed.

Do the Balkans have any right to laugh at this? We have no throne, but we have plenty of institutions where someone with obvious ability waits outside the door while the decision inside is made by a rule written generations ago. The only difference is that here the rule is less often called tradition, and more often called an arrangement.

In 2033 Ise will be torn down and rebuilt again, as it has been for thirteen centuries. The question is whether by then anything will have changed in the text that decides who may stand closest to the mirror.