It's Saturday night in downtown Tokyo. There is little evidence of the political and economic turmoil gripping Japan as thousands of revellers cram into overcrowded commuter trains after a hard evening on the town.
There is no limit on the number of passengers packed into trains and subways in this, one of Asia's most populated cities. In fact, rail company staff wearing white gloves are employed specially to push as many people as possible on to the already overcrowded carriages.
Tokyo boasts one of the most efficient train systems in the world. They are clean, fast and on time, and in the rare event of a delay in the morning rush, rail companies issue apology slips to office workers to show their bosses. In Japan, punctuality is everything.
But on the crowded trains there now lurks a hidden menace of huge concern to the authorities and the female population of Tokyo, the chikan.
Chikan means "dirty old man" or "pervert" and is the name given to train molesters who have become a social scourge in Tokyo. The overcrowded train carriages present the chikan with the perfect hunting ground for his seedy activities.
Figures published last week show that 1,854 alleged train molesters were arrested by Tokyo police last year, with approximately half that number being charged. But police say the figure is not an accurate reflection of the problem, as many women are still reluctant to report the offence or to seek help from fellow passengers.
Women are most likely to be fondled in the morning rush-hour between the hours of 7 a.m. and 9 a.m., or late at night at weekends after businessmen "let themselves go" in city bars.
The notorious Saikyo line produced the highest number of arrests in 2000 for the fourth year running, with 79 molesters detained. The Yamanote line which circles inner Tokyo had 20 arrests last year.
During morning rush-hour the Saikyo line runs from Ikebukoro to Shinjuku at over 230 per cent capacity. According to the police, it is a molester's paradise and home to a group of "gropers" who target high school girls. Young female commuters have nicknamed the line the "molesters' train".
The gropers' favourite starting point is Shinjuku station, where nine trains and two subways churn out an incredible 2 1/2 million passengers a day.
Shinjuku is the city's most vibrant district, and a place of extremes. It's the centre of corporate and social activity with its huge skyscrapers and neon-lit bars. But it also has the highest concentration of homeless people in Tokyo.
Around the local train station, people swarm in such numbers that progress is at a snail's pace. It is easy to see how gropers can operate with impunity in the vast crowds.
The train companies themselves are trying to take action on the problem. From March 27th the Keio Electric Railway, which runs a private train line from outlying districts to the city centre, is introducing special women-only carriages on eight of its express trains leaving Shinjuku after 11 p.m. at weekends.
Women-only carriages, introduced by the company on a trial basis during Christmas, were hailed as a great success.
According to the Tokyo Women's Plaza, women in the past viewed subway gropers as just another commuting hazard. If they complained, they would have been blamed for what happened.
One recent survey undertaken by the group showed that 72 per cent of female high school students said they had been molested on a train more than once. But 40 per cent said they had confronted their harassers.
The association spokeswoman, Ms Keiko Aoki, said the younger generation were prepared to attack the chikan physically. "I saw one young woman on a train grab a man and twist his arm."
The plight of harassed women has been taken up recently by a Tokyo insurance company. Tokyo Marine introduced an anti-stalker insurance policy last month called "Lady Guard".
The company says sales of their new product have been strong. The policy will provide services such as collection of evidence and physical protection for women who fear they are being stalked or harassed.
But the fight-back by women has resulted in claims from aggrieved men of being falsely accused of molestation. In Tokyo last year there were some 20 disputed cases, according to the People's Aid and Relief Association of Japan, a group supporting those who say they've been falsely accused.
The association says the actual number of false charges is higher than the number of court cases, since many of those accused in the wrong wind up signing confessions just to end the process.
"We receive a number of calls from falsely accused molesters who, even though they did nothing, confessed to the police for fear of losing their job," a spokesman said.
Although incidents of rape and other violent crimes against women are still rare in Japan, sexual harassment is a problem. It is still a male-dominated society, but things are changing, slowly.
At least when it comes to the train gropers, Tokyo's women commuters are beginning to speak up after years of suffering in silence.