Crown Prince Naruhito, who will in time ascend the throne as Japan's 126th Emperor, will also inherit the role of rewriting the rulebook of the world's oldest hereditary monarch.
His father, Emperor Akihito, 82, is known for a series of firsts. Among other things, he was the first in a bloodline extending more than 2,500 years to marry a commoner, and he has a pet cause in science. The Crown Prince also married a commoner - in 1993 - after a dogged on-off courtship that lasted seven years. His wife, Crown Princess Masako, 52, was a high-flying career diplomat who turned him down twice before agreeing to take his hand in marriage.
The 56-year-old is also a fierce champion of water conservation issues, and frequently attends water conferences abroad. And like his father, Crown Prince Naruhito - whose name comprises words that mean "benevolent" and "virtuous" in Japanese - harbours staunch views that Japan needs to learn lessons from its wartime past.
He joined his father in making remarks on the 70th anniversary of the end of World War II last year, in what was widely seen as a pushback against Japan's tilt to the right.
He said then: "Today, when memories of war are set to fade, I reckon it is important to look back on our past with modesty and pass down correctly the miserable experience and the historic path Japan took from the generation who know the war to the generation who don't."
Crown Prince Naruhito, who graduated with a history degree from Tokyo's Gakushuin University and has a doctorate in civil law from Oxford, has an independent streak that is sometimes at odds with the rigid, austere lifestyle imposed on royals by the bureaucratic Imperial Household Agency.
The royal love story had, reportedly, involved him sneaking out of the Imperial Palace in a curtained van to meet his future bride, to avoid his minders and media glare.
And in a rare public spat in 2004, he told his agency minders to back off as he insinuated that they were behind a stress-related breakdown suffered by his wife, which resulted in her shying away from public appearances. He said: "It's true that there were moves to deny Masako's career and her personality."
Though he later apologised for the outburst, he argued for "new royal duties" that befit the 21st century.
Last Monday, Emperor Akihito hinted at his desire, given his age, to step down from the throne in favour of his elder son.
In an address to millions of Japanese for only the second time in his 28 years of reign, the revered monarch said it was impossible to "reduce perpetually" his workload. He added that he had "wondered from time to time" if it was possible to prevent society from coming to a standstill in the transition period between eras when an emperor dies, as is the case now.
The Crown Prince, who was on a visit to Aichi prefecture, is said to have watched the broadcast in a VIP room at the JR Nagoya train station. His aides said he is taking his father's message "very seriously".
Japan will form an expert panel as early as next month to deliberate on changes to the Imperial Household Law to allow the Emperor to step down.
Next in line following Crown Prince Naruhito is his younger brother, Prince Akishino, 50, and then the latter's son, Prince Hisahito, now nine.
The Crown Prince and Crown Princess have one daughter, Princess Aiko, 14, whose name was chosen by the couple instead of the Emperor in a break with tradition.
But she cannot ascend the throne as laws were rewritten in 1889 to allow only men to do so. Japan has had seven female monarchs, the last of whom ruled in 1770.
An expert panel was formed in 2005 to look at how to change the law to allow female succession, but talk of this stalled in 2006 following the birth of Prince Hisahito.
Remarks made by the brothers in that period have widely been interpreted to imply a rift in the royal family, though both are understood to have mended fences.
Prince Akishino had openly criticised his elder brother over his publicly aired grievances in 2004, and a year later he said he seldom talked to the Crown Prince.
"Regarding communication with the Crown Prince, we are not visiting the Crown Prince's household actively from our side... since the Crown Princess is sometimes feeling good and sometimes not," Prince Akishino said in December 2005. "We will come over whenever they call us."
Two months later, Crown Prince Naruhito hinted at his mixed feelings over the prospect of a baby boy who could trump his daughter's chances for the throne.
"As a parent, there are many things that go through my mind. But I would like to refrain from further comments," he had said when asked about his daughter's future.
The Crown Prince wedded later than his younger brother, fiercely resisting pressure to get married in 1990 by saying: "I know how to operate a washing machine without getting covered in bubbles, and I know how to handle an iron. I will be going about it at my own pace, without hurry - I don't feel guilty about being single."
Four years earlier, he had met his bride-to-be at a concert. Crown Princess Masako is a Harvard graduate who spent 14 years of her life overseas and can speak six languages. She agonised for eight months over whether to give up her career for the sedate royal life.
And she has had trouble adapting. Besides her stress-related breakdown, local media, which once described her as a "sassy ambitious woman" with the North American directorate at the Foreign Ministry, has since called her a "dowdy, public shadow of her former self who walks three steps behind her husband".
A question mark still lingers over whether she is capable of succeeding her mother-in-law as Empress.
Even today, she has not assumed her full share of royal duties although she has increased her public appearances of late. Just last week, she visited Nagano prefecture to mark the new Mountain Day public holiday with her husband.
This article was first published on August 15, 2016.
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