A remark by Prince Akishino, who will become first in line to the throne next year, has stirred controversy over how freely members of the Imperial family can speak about contentious matters because the Constitution prohibits the head of the family from being involved in politics.

In a rare move for a royal, Prince Akishino, second son of the outgoing Emperor Akihito, questioned the government's decision to use a massive amount of public money for a Shinto-related ritual to take place in November next year as part of the ascension of Crown Prince Naruhito.

"I wonder whether it is appropriate to cover the highly religious event with state funds," the prince said during a recent news conference for his 53rd birthday, baffling senior bureaucrats of the Imperial Household Agency as well as many experts on royal family matters.