Image copyright TOSSAPOL CHAISAMRITPOL/BBC THAI Image caption A republican protest on the week of the coronation attracted little public attention

Earlier this week, as Japan was preparing to mark the historic abdication of one emperor and the enthronement of the next, a small group of people gathered on the edge of Tokyo.

"Let's not forget the war responsibility of the emperor," the protesters chanted as they marched towards a park.

The group, mostly grey-haired, belong to a small but vocal minority of Japanese people who think the time has come for the age of emperors to end.

Image copyright TOSSAPOL CHAISAMRITPOL/BBC THAI Image caption 'Nomura' admits it is a challenge recruiting new support

Japan claims to have the world's oldest continuing monarchy. According to legends, the royal family are descendants of the sun goddess Amaterasu.

Until the end of World War Two, emperors were seen as living gods.

Han Tennosei Undo Renraku Kai (Anti-Emperor Activities Network), or Hantenren, have been calling for the abolishment of the monarchy for more than three decades.

They say it's the only way for Japan to atone for the wars waged in the name of the emperor in the 1930s and 40s.

"The war hasn't been put to an end properly," Nomura, a Hantenren member, told the BBC. He asked to be referred to only by his surname, for fear of attacks by right-wing groups.

Image copyright AFP Image caption Wartime Emperor Hirohito renounced his divine status after Japan's defeat

Sitting in the tiny office of the protest group in central Tokyo, Nomura said wartime emperor Hirohito was a war criminal who committed crimes against humanity during World War Two.

"Hirohito had strong interest in the military. He was only afraid of wars with the US and UK because he knew Japan was militarily inferior to them," says Nomura. "He didn't hesitate to wage war in Asia."

Hirohito's war responsibility is still debated by historians.

Image copyright AFP Image caption Emperor Emeritus Akihito is a beloved figure in Japan

After Japan was defeated, Hirohito, who sat on the Chrysanthemum Throne from 1926 to 1989, renounced his divinity.

Under the constitution written by the US, Japan became a constitutional monarchy with the emperor kept on as "symbol of the state" who is forbidden from being involved in politics.

The preservation of the emperor system means Hirohito was never made accountable for his role in the war, says Nomura.

Peace-keeping symbol

In the later years of Hirohito's reign, anti-monarchy feelings were more pronounced. Leftist radicals carried out occasional small attacks on places associated with the emperor.

But his son Akihito, who abdicated this Tuesday because of his age and ill health, succeeded in establishing the royal family as a symbol of peace after coming to the throne in 1989.

Now called Emperor Emeritus, Akihito was 11 when his father announced Japan's defeat on radio - the first time most Japanese had heard his voice.

"Akihito's signature issue was trying to bring closure to the post-war period by trying to heal the lingering wounds from the wartime," says Ken Ruoff, director of the Center for Japanese Studies of Portland State University in the US state of Oregon.

"He did whatever he could to improve relations with countries victimised by Japan."

Image copyright Reuters Image caption Akihito and Michiko mourn the victims of the Battle of Okinawa during a visit in 1975

In 1975, Akihito, still the crown prince at that time, made an unprecedented trip to Okinawa - one of the bloodiest battlefields in Japan where more than 100,000 civilians perished - with his wife Michiko. The royal couple was attacked by activists, but was unharmed.

Akihito also visited war-ravaged countries including China and Indonesia and, though barred from commenting on politics - repeatedly called on his people to remember the horror of war.

Some of the countries worst affected by Japan's wartime atrocities maintain the country has never fully apologised or atoned for its actions, and the period remains deeply controversial.

But domestically, under Emperor Akihito, the royal family has became immensely popular. In polls and surveys, about 70-80% of the people support keeping the monarchy, according to Mr Ruoff.

Dwindling support

In his office in Tokyo, Nomura admits that the group has been losing supporters over the years.

In the 1980s, one rally could attract some 3,000 protesters, but they're having problems attracting new blood.

At Monday's rally, the 80 or so protesters were outnumbered by the hundreds of police deployed to contain them. Few onlookers paid them much attention.

Image copyright TOSSAPOL CHAISAMRITPOL/BBC THAI Image caption Protesters were vastly outnumbered by police during Monday's protest

Nomura says it can get lonely fighting for an unpopular goal, but that it's important to educate the public about the problems a monarchy could bring.

"Japan is now in a national identity crisis because the economy is in decline," he said. "The current government led by Shinzo Abe and the right-wing believe that the emperor can lend legitimacy to them."

He plans to continue his activism for another 10 years or so, as long as his health permits.

But he faces an uphill battle. Japan's imperial line goes back more than 2,000 years, and the role of emperor is tightly bound with many aspects of Japanese culture.

A new emperor coming to the throne - with a touching transfer of power from the beloved outgoing monarch - has generated a wave of affection, and has probably put a seal on the republican debate, at least until the throne becomes vacant once more.

Additional reporting by Grace Tsoi