It is an early Saturday evening and Akihabara - known around the world as the place to go in Tokyo for the latest electronic gadgets and "otaku" collectibles - is thrumming.
Neon flashes and barkers entice passers-by with offers of the newest releases. The area around the station is packed with people leaving with their purchases and others arriving to join the melee.
Akihabara sprawls over several blocks in all directions, but consumers are not only here to purchase hardware.
Tsukumo Dori runs parallel to the main thoroughfare in Akihabara, but is a narrower street lined at ground level by stores selling every conceivable electronic device. About a decade ago, however, a new type of seller appeared here.
Today, every couple of meters down both sides of the street are girls in their mid-to-late-teens handing out fliers and encouraging male passers-by to step into a nearby stairwell that will take them to a "cafe" on an upper level.
They wear schoolgirl uniforms with revealingly low skirts and their shirts are undone at the neck; others wear clothes similar to those worn by famous "manga" characters. More menacing are the young men who stand back and monitor what the girls are doing.
These men similarly work for the numerous cafes that dot the area, but they're not interested in the front business of young women in costumes serving coffee and cake.
They are motivated by the far more lucrative income from the services that are not on the menu but can be quietly negotiated later. The shop encourages its girls to go on what is termed a "Joshi kosei (JK) osampo," which literally translates as going for a walk with a high-school girl.
The price of a 30-minute stroll with a girl in uniform is around 5,000 yen (37 euros), of which her shop will take half. Other options include the girl hugging the customer, slapping him or laying next to him - although the shops say that no sexual acts are allowed.
Given the easy money available, the girls quickly learn to freelance and a customer can ask for the "Ura op," or secret menu.
The owners of the cafes are able to deny all knowledge and say they are merely offering a legitimate service, but Yumeno Nito, who used to work at a maid cafe, is adamant that they are responsible.
"Japan is not an advanced nation when it comes to our understanding of the problem of child prostitution," said Nito, who fled a troubled home life as a teenager and worked for a time in the Shibuya district of Tokyo.
"In Japan, the 'joshi kosei' business is looked at as trendy or a form of entertainment," said Nito, adding that society here is becoming ever-more tolerant towards youngsters employed by the sex industry, while the media treat the latest fads as fodder for titillation.
And that means there is virtually no assistance for any of the girls who realize that they are in danger. One of the few exceptions is Colabo, a small volunteer organization that Nito set up after meeting a pastor who helped her leave her past behind.
"The sense in society here is that it is the girl who is in the business who is bad, that it is her parents who have failed and there is no blame attached to the person who 'buys' the girl."
The pimps who come up with the steady stream of young girls required to feed the apparently insatiable demand for sex in Japan are "very clever," Nito says.
Easy prey for pimps
"Most of these girls are easy prey," she said. "Some have mental disabilities, others have issues involving low self-esteem, others are self-abusing or have attempted suicide."
Around 30 percent are simply from very poor homes and tell stories of having to take a part-time JK job just to buy their school lunch. A similar proportion come from broken homes or have been abused.
So the pimps befriend them, lend a sympathetic ear to their stories and buy them a meal or two. Short of cash, runaways or abused girls keep coming back and the pimps buy them clothes and even let them sleep on the sofa in their office from time to time.
Then they offer them an easy way to make some cash and the girls - who by now trust their new friend - leap at the opportunity to be independent.
Most worrying to Nito are the remaining 30 percent, who come from stable homes but are tricked into the business after replying to job offers on social media sites that sound legitimate.
"These are the children who are trusting of adults and do not understand the harsh realities of life," Nito said.
As we walk through Akihabara, a Colabo volunteer quietly points out a reflexology shop that is really a front for the JK business while nearby a video store stocks child pornography.
"My feeling is that child pornography is an extreme case and the majority of Japanese society is disgusted by it," Makoto Watanabe, a lecturer in communications and media at Hokkaido Bunkyo University, told DW. "But it is available," he admits.
Japanese media to blame?
"But I believe this whole JK business has been enhanced by the Japanese media," he said. "Television programs constantly seek new, younger faces and even in the past 10 years or so there has been a clear decline into what could be described as soft porn on mainstream TV here."
This takes the form of bands such as AKB48, which is made up of teenage girls who perform in a variety of revealing costumes and who frequently appear in advertisements in similarly skimpy outfits.
"That looks abnormal in the West, but it has become mainstream here and nobody even thinks about it any more," Watanabe said.