By Jonathan Head
BBC Tokyo correspondent
It's just before nine o'clock in the morning at Shinagawa station, one of the main entry points for the millions of commuters who come into Tokyo every day.
There are few non-Japanese faces to be seen in Japan
There is a seemingly endless sea of people pouring off the platforms, on their way to work.
The most striking aspect about this is how similar everybody looks - Japan is still one of the most ethnically uniform societies on earth. It accepts very few immigrants.
But as the population ages and shrinks, many business leaders here are arguing that this has to change.
At one of several old-people's homes outside Tokyo, residents are having a karaoke sing-song.
It is one of several homes run by a company called Riei, which is doing very well out of Japan's ageing society - so well that it is always chronically short of staff. The obvious answer might seem to be to recruit from overseas.
There are only two foreign employees at the home. One of them is Chonlada, from Thailand, who is allowed to work only because she is married to a Japanese man.
Riei's president, Hajime Kabasawa, is frustrated with the strict rules on immigration and wishes his country would ease the restrictions.
"I understand why people oppose immigration. They're frightened of crime and unemployment, but we have to think of the benefits. Bringing in foreigners to do these kinds of jobs will allow skilled Japanese to work in other sectors of the economy," he said.
Three thousand miles away, there is another sing-song under way, this time by a group of young nurses in Bangkok. They practise popular Japanese melodies with Hajime Kabasawa's son as part of a training scheme that they hope will eventually lead to jobs with Riei in Japan.
"This programme teaches us Japanese language and customs," said 19-year-old Saowarak Thassada, who comes from a poor village in north-eastern Thailand.
"I'm studying here because my dream is to go to Japan - I hear there are lots of elderly people there with no-one to look after them. I'd like to help them and become their friend."
However hard they train, there is no chance they will go to Japan any time soon. The two governments have been discussing letting more Thai workers in for months as part of a free trade deal.
But Japan is reluctant, because of deep-rooted fears about the impact more immigrants might have on their sheltered society.
"When unskilled workers come to Japan they'll bring their families with them. The number is bound to increase," said Jinen Nagase, a senior member of the governing Liberal Democrat Party who sits on the party's labour committee.
Japan is looking at incentives for people to have more children
"They'll create slums and boost the population of uneducated people. And eventually they'll demand the right to vote - these are problems European countries are facing now - that's why we are so cautious."
A long queue snakes around the Tokyo immigration centre from early morning. People like Letitia, from the Philippines, who have overstayed their visas, have come to be voluntarily deported from Japan, in the hope they will not be black-listed on a permanent basis.
"Here in Japan, money is very high compared to the Philippines. Most Filipinos' dream is to come to Japan or America, mostly those two countries."
Japan, though, shows no signs of lifting its fortress-like barriers against immigrants. Last year just 15 asylum seekers were given refugee status - a fraction of those accepted by most developed countries.
But public opinion is slowly beginning to change.
"It's obvious that we need more workers," said Nakasayu Ando, a dealer in antique samurai swords, who holds conservative views on most issues.
"And I think bringing them in from overseas would actually help stimulate our economy - like in America, immigrants end up making money and then spending it here in Japan."
The residents at the Riei retirement home, relaxing perhaps for the first time after a life of relentless hard work, are unwitting actors in Japan's demographic drama.
Every year, there are many more of them, and many fewer people to care for them. Just how much longer can the government keep its doors closed to the millions outside, who would willingly plug the gap?