Emperor Akihito hinted that he wants to abdicate, but the move would be unprecedented under Japan's Imperial House Law, which says an emperor serves until death. (Jenny Starrs/The Washington Post)

Japan’s popular emperor sent an unprecedented signal Monday of his desire to abdicate and hand over power to his son, steering the country into constitutionally uncharted waters.

In a televised video address to the nation — only the second time an emperor has spoken to the people that way — 82-year-old Emperor Akihito described how his declining health was curtailing his abilities to fulfill his obligations.

“When I consider that my fitness level is gradually declining, I am worried that it may become difficult for me to carry out my duties as the symbol of the state with my whole being as I have done until now,” Akihito said. The first time he addressed the people in a recorded video message was after the 2011 tsunami, which claimed almost 16,000 lives.

Akihito’s announcement was not a surprise. He has had health troubles — prostate cancer and heart problems — and, marking his birthday in December, he said there had been times when he had felt his age.

But there is no legal provision for him to step down. The parliament will have to decide whether to amend the Imperial Household Law, a process that could take years.

People watch a large screen showing Japanese Emperor Akihito's video address in Tokyo on Monday. REUTERS/Kim Kyung-Hoon (Kim Kyung-Hoon/Reuters)

Prime Minister Shinzo Abe said afterward that he took the emperor’s statement “very seriously.”

“As for the way the emperor’s duties are done, when you consider his age and the current burden of his duties, I think we will need to give a thought to the emperor’s anxiety and to think well what we can do,” Abe told reporters.

Toshihiko Saitou of Gakushuin University, author of the book “Emperor Akihito and Pacifism,” said the government “can’t ignore his intention but must act on his words.”

Under the U.S.-drafted constitution imposed on Japan after World War II, the emperor was stripped of all his powers, becoming a figurehead only.

The emperor is also legally constrained from saying anything political, and that means that Akihito could not declare his intention to step down — which could be construed as a political statement because it would require a parliamentary amendment. Instead, he had to speak in oblique terms.

Still, his message was clear. He said that simply making his son, Crown Prince Naruhito, a regent would not be sufficient because neither the retired emperor nor his regent would be completely fulfilling the emperor’s duties.

“In coping with the aging of the emperor, I think it is not possible to continue reducing perpetually the emperor’s acts in matters of state and his duties as the symbol of the state,” Akihito said, according to an official English translation of his remarks, which were aired on NHK, the public broadcaster.

But having a regent would “not change the fact that the emperor continues to be the emperor till the end of his life, even though he is unable to fully carry out his duties as the emperor.”

Akihito clearly does not want to do only half the job, analysts say, and carefully parsed his words so as to convey this.

Professor Hidehiko Kasahara of Keio University said the emperor was trying to express his personal desire to retire without saying the word “abdicate.”

“He sent out a strong message that he’d like to hand over to his successor and wants him to stably continue the duties as the symbol of the state,” he said. “Since he doesn’t hold any right to get involved into politics, he chose this way to talk about his opinion as an individual. And that must have reached people’s hearts very heavily.”

Akihito, who has previously signaled that he supports the pacifist constitution imposed on Japan after the war, is the only emperor to have been sworn in under it and is widely viewed as being opposed to Abe’s intention to loosen some of the country’s postwar shackles.

Akihito has been on the Chrysanthemum Throne for 28 years, since the death of his father, Hirohito, who ruled Japan throughout the brutal wartime period and after. Hirohito, who broke tradition and delivered a famous radio address to his people in August 1945, announcing Japan’s surrender in World War II, died at age 87; Akihito was 55 when he succeeded his father. His oldest son, Naruhito, is 56.

Last month, NHK reported that the emperor wanted to abdicate, although the Imperial Household Agency denied the report. Some analysts thought the government had leaked the information to test the public response.

Polls have since shown that the public is supportive, with between 77 percent and 90 percent of respondents saying the government should create a system to allow the emperor to abdicate.

Although the emperor has few powers, he holds a special place in Japanese people’s hearts.

Japan has had centuries of emperors — surviving eras of powerful samurais and shoguns and wars — who were considered to be divine and direct descendants of Amaterasu, the Shinto goddess of the sun. Today, however, the emperor serves as a unifying figurehead.

Abdication was relatively common until 1817, when Kokaku became the last emperor to resign his post. No provision for abdication was included in the constitutional and legal changes following Japan’s surrender at the end of World War II.

Yuki Oda contributed to this report.