By Roland Buerk
BBC News, Tokyo
The Communist Party has always had a surprisingly large role in Japan
The protesters gathered in a park in the shadow of corporate headquarter skyscrapers, a short walk from Ginza, Tokyo's most upscale shopping district.
Hundreds strong, they included workers already laid off as the global downturn battered Japan's economy, and those who feared they might be next.
The demonstrators set off on a march towards Japan's Diet building - or parliament - carrying red flags.
"I support the Communist Party because it's the one that thinks about workers first," said one man.
"We're demonstrating to get better rights for the temporary workers," said another.
"The Communist Party is the only party that gets really serious about problems like this."
Fists in the air
Lined up on a set of steps near the Diet, wearing suits, red sashes and beaming smiles were officials from the Japanese Communist Party.
They joined the protesters chanting and raising their fists in the air.
The Communist Party has always had a surprisingly large role in Japan, the world's second biggest economy.
But while it had been fading towards irrelevance, now as the recession bites it is on the rise again.
The party already has more than 400,000 members and people are joining at the rate of 1,000 a month.
In comparison, the membership of the Liberal Democratic Party, the largest member of the governing coalition, is twice the size. But its numbers are declining.
"Many people are beginning to think: 'Is Japanese capitalism OK as it is?'" said Akira Kasai, a Communist member of the Diet's House of Representatives.
"Living standards are going down. The gap between rich and poor is growing."
Communist ideology has been spread in Japan in unusual ways.
There was a book, Kanikosen - The Crab Factory Ship, which raced back up the bestsellers' lists.
A classic tale of proletarian fishermen uniting to rise up against their bosses, it had been almost forgotten since it was written in 1929.
Some new followers discovered Communism on the internet
Publishers have also produced a manga, or comic, version of Das Kapital, Karl Marx's treatise on how capitalism would collapse under the weight of its own contradictions.
One new Communist Party member we met in a restaurant found out about Marxism on the internet.
"I got interested in Karl Marx a few years ago," she said.
"In capitalism now we are controlled by the capitalists, or capital. But I think in communism society we can think about whole of the society and decide our economic activities in democratic way."
The woman, 34, did not want to be identified for fear her employers, whom she claimed disapproved of the Communists, would find out.
But she had told her family.
"My parents were very surprised that I joined the party," she said. "They are not supporters of the Communist Party. They don't understand correctly, I think."
The woman said she was a member of a "lost generation" - people who came into the employment market during Japan's long stagnation in the 1990s and could not find proper jobs.
As the economy picked up at the start of this century, employers picked graduates untainted by years of drifting.
Now Japan's economy, which relies for growth on sales abroad of cars, electronics and machinery, is struggling again.
Exports have fallen by nearly half compared to a year ago, and industrial production has dived.
The traditional Japanese dream of a job for life has been further undermined by reforms of the labour market in 2004 that allowed manufacturers to take on temporary workers.
About a third of the workforce is now on short-term contracts and their jobs are the most threatened.
Communist members of parliament make much of their efforts to get workers a better deal by holding talks with company managers.
Unions are helping some to take their employers to court claiming wrongful dismissal.
Not even the Communists themselves expect to win power soon.
But they won nearly five million votes in the last election for the more powerful lower house of the Diet, and that was before the downturn.
They are hoping to do better when the Japanese next go to the polls later this year.
"Of course the final goal is a socialist, communist society in Japan, overcoming capitalism," said Akira Kasai.
"But before that we are taking a step-by-step approach. The first stage is to solve problems of labour and living standards according to people's demand."