Crown Prince Naruhito, who is the next in line to Japan's Chrysanthemum Throne, is one of the fiercest critics of the cloistered monarchy institution he belongs to.
The 56-year-old Oxford University alumnus has an independent personality at odds with the rigid lifestyle that is imposed on royals by the bureaucratic Imperial Household Agency.
In one of their most documented spats, he accused his minders of causing his wife, Crown Princess Masako, to suffer a stress- related illness.
His father, Emperor Akihito, was the first monarch in a long bloodline extending 2,500 years to marry a commoner, and the Crown Prince did likewise when he married the former diplomat in 1993.
In 2004, he went public with his displeasure at the agency for stopping him and his wife from travelling overseas.
The agency had felt that the Crown Princess' primary duty was to produce an heir to the throne.
They have a daughter, Princess Aiko, now 14, but the antiquated Imperial Household Law allows only males to inherit the throne.
Naruhito later apologised, but he also called for "new royal duties" befitting the 21st century.
Also like his father, the first peacetime monarch, he has urged Japan to learn from the lessons of its wartime past. In remarks last year to mark the 70th anniversary of the end of World War II, he said: "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."
These remarks were seen as a rebuke to the shift to the right by the ruling Liberal Democratic Party (LDP) government.
The Crown Prince regularly attends conferences on water policy and water conservation abroad, and is a sportsman and music lover. The Imperial Household Agency website describes him as "an avid tennis player (who) also enjoys mountaineering and jogging. He is an accomplished violist".