TOKYO -- Emperor Akihito, who has delighted millions of Japanese by setting precedents both before and after his reign began in 1989, devotes today to a first he might prefer not to set.
This is the 31st birthday of his eldest son, Prince Naruhito, and the day the young heir is being installed officially as crown prince -- the first bachelor to become designated successor to the throne in the world's oldest royal lineage.
"It's simply never happened before," said Ben-Ami Shillony, professor of Japanese history at the Hebrew University of Jerusalem.
"For centuries, the practice was that the emperor's first son was assigned a bride, chosen by the court bureaucrats, in his teen years, with the goal that he should already have sons by the time he acceded to the throne," Mr. Shillony said.
Like his father and his grandfather, Emperor Hirohito, Prince Naruhito keeps his scholarly, artistic and fitness credentials polished. He studied at Oxford, plays tennis and the viola, and climbs mountains.
The crown prince's prolonged bachelorhood is of scant political significance but is potentially a threat to the continuity of the imperial line, which many Japanese consider central to the emperor's role as symbol of the nation.
It also has provided the country's many sensation-mongering magazines and personality-hungry television shows with a decade-long excuse to set up camera ambushes outside the homes of wealthy or socially prominent young women whose names have been linked, seriously or spuriously, to Prince Naruhito's.
In the 10 years since he began to be considered eligible for marriage by modern imperial household standards, the list has lengthened steadily to include six dozen women.
Many are members of brand-name families as familiar to the outside world as Mitsui or Toyota. Others, though far from household names outside Japan, are widely followed by society watchers here as descendants of ancient noble houses.
Once on the pop-magazine list of "possibles," it can be hard to get out of the spotlight, as several young women have discovered even after marrying other men or moving away from Japan.
Interspersed with articles on these Japanese "candidates" have been occasional in-depth analyses of "clues" to the prince's feelings. One report that he had pinned up a poster of actress Brooke Shields in a bedroom during his student years has been the basis of endless speculation that he doesn't marry because no one can fill her place in his heart.
The precedent Prince Naruhito sets is a direct product of one of the most celebrated precedents set by his father, who was both the first crown prince ever to choose his own bride and the first in centuries to marry outside Japan's minuscule and deeply inbred aristocracy.
Emperor Akihito's marriage to Empress Michiko was a storybook romance, starting on a tennis court. But it was followed by decades of reports on the austere and bureaucrat-driven life of Empress Michiko.
His parents' marriage thus gave Prince Naruhito, on the one hand, the freedom to choose his own bride and, on the other, the problem of reportedly finding that many eligible young women think twice before giving up their freedom to marry the heir to the throne.
While the crown prince has been unable to solve what he has called "this problem," his younger brother, Prince Akishino, courted and last year married Kiko Kawashima.
As a bride and now as a princess, she has proved to be almost as popular as her mother-in-law, casting into even deeper relief the fact that her older brother-in-law remains a bachelor beyond 30, the age he himself set in an interview six years ago as the time for a crown prince to be married.
"Prince Akishino," a pop magazine wrote last month, "has the advantage of being one step away from the limelight and thus able to offer a bride a life perhaps just free enough to be still attractive."