Here, "high school dating" matches girls in uniforms with men in their 40s and 50s and beyond. And it means money changing hands.
Sometimes this involves a walk around the block or a drink in a bar. More often, it involves sex - child prostitution by another name.
"It's easy to talk to these girls," said one man in his 30s who was sitting at a wooden school desk in AKB High School, a cafe in Akihabara, a part of Tokyo known for its subcultures. A 17-year-old girl in a school uniform brought the man and his colleague, both of whom declined to give their names, beers and chitchat.
"We actually find regular bars uninteresting these days," he said. "I got tired of regular bars with old women."
They admitted that the uniforms are a big part of the attraction. "They look so cute," said his friend, in his 40s. "The uniforms make them look one and a half times cuter than they actually are."
This is Japan's shady "JK" or "high school dating" business. ("Joshi kosei" means "high school girl" in Japanese, and the English initials JK are universally used here to describe the practice.)
Although some cafes like this are relatively innocent - those that employ high school girls must close by 10 p.m., which means the men aren't too late getting home to their wives - there is a large part of this world that is not.
There are various levels of high school dating, starting with cafes staffed by underage girls and peep shows where high school girls sit behind a one-way mirror in their school uniforms, posing according to customers' requests.
There is also "tour guiding," when girls go for a walk with men, a walk that often ends with some kind of sexual service, and the straightforward "compensated dating" - being paid for sex.
Kazue Muta, a professor of sociology and gender studies at Osaka University, said the element of taboo makes girls in school uniforms sexually attractive to men. "Japan is a patriarchal society, and it has this mentality that the young and seemingly innocent are valuable and more alluring," she said.
In its most recent report on international human rights practices, the State Department noted concerns about the sexual exploitation of children in Japan, saying that "compensated dating" in particular facilitates the sex trafficking of children.
Some efforts have been made in recent years to curtail the business, but they have amounted to little - partly because so few people consider it a problem.
Yuki Aoyama, a photographer known for his "schoolgirl complex" pictures, said the way he sees it, it's just a business.
"There are men who want to spend time with high school girls, and there are girls who want to make money," he said.
One of the people trying to do something about it is Jun Tachibana, from the nonprofit Bond Project, which is trying to get girls off the streets and stop them from falling into the JK business.
Tachibana and two colleagues were out on patrol on a recent night in the busy area around Shibuya, its neon-filled streets lined with cheap restaurants and fast fashion, looking for girls who might be in trouble.
"Hi," Tachibana said, approaching a girl crouching in a busy meeting place near the Shibuya train station exit, her shoulders hunched over, carrying two bags. She had the look of a girl who didn't want to go home that night.
Tachibana recognized her as a 17-year-old they had found in this area before. "Why don't you go home? I'll see you off at the station," she said, offering to accompany the girl to the tracks. But the girl refused.
"Well, at least stand up so you don't look so vulnerable," Tachibana said.
"There are girls in difficult situations - they could be coming from a poor family or could be sexually abused at home - and find it hard to live their lives," Tachibana said. "Some say they are so lonely that they want to die and disappear. Often these girls don't have a place to stay, so they get into the JK business."
This night, Tachibana had some luck. She returned to the meeting place later and persuaded the girl to go home. "My job is done tonight," she said. "I've been successful with one girl."
But getting girls off the street one by one will not make much difference when there is still so much demand - particularly for those still in school.
One of his businesses involved peep shows where girls between 15 and 17 years old sat in their school uniforms folding paper cranes, their legs arranged so their underwear was visible. Men paid $60 to watch a girl of their choosing for 30 minutes.
"Many Japanese men find something erotic in a school uniform," Taka said. "They are disappointed if they find out she's not still at school."
Girls involved in the JK business are insistent that they choose to do this work, and Taka says it's not exploitation because the girls want to be in the business. "When we recruit for girls under 18, we're flooded with applications."
Mio, a 17-year-old in her second year of high school in Tokyo, started in this business last year, having sex with a man in a karaoke room for $30.
"When I'm at home at night, I get lonely and want to be needed by someone. That's when I do it," said Mio, asking to be identified only by her work name.
Now she posts on a messaging app on weekends - when she's not at dance or band practice - and finds an eager audience, sometimes college students, sometimes men in their 50s, the same age as her father.
Once, a man choked her during sex. Another, she said, "wouldn't stop when I said no." But generally, the men treat her well, she said.
"I feel accepted and needed, and I don't have these feelings otherwise," Mio said over lunch, wearing the fresh face and oversize sweater of any other teenager. But she described a home life where her parents hate each other and she hates them. "I wish I could stop. I might be able to stop it if I don't feel lonely anymore."
Advocates for girls say this practice is nothing short of child prostitution.
"Some girls tell me it's as easy as working at a karaoke or a fast-food store, but that's not right," said Yumeno Nito, a 27-year-old who runs Colabo, a support group that helps exploited girls. "They are talked into believing that this is the same kind of work, by adults who treat them kindly at first to lure them into the business."
Nito's group has helped girls who have been raped or assaulted and girls with mental or learning difficulties who are talked into doing degrading things because they think it will make them feel worthwhile. Depression and mental instability are rife.
Even if ordinary Japanese consider the practice deviant, they place the blame on the girls, said Muta, the sociologist. High school girls who become pregnant are regularly expelled from school.
"They think this can't be helped because these bad girls exist," she said. "Many people see it as a problem with the girls, not with the men."
As such, when authorities discuss ways to curb the practice, they tend to come up with ideas such as imposing curfews on girls, rather than penalizing men for having sex with high schoolers, Muta said.
Regulations have been tightened slightly in recent years to address exploitation. Girls were banned from officially working in "high school girl" stores in 2014, but many still do. There's even a word for them in the advertising: "under," as in "under 18."
Legislating will not solve the problem, said Tachibana of the Bond Project.
"These girls are still children, and what they are going through is sexual exploitation," she said. "But imposing stricter regulations will just push these activities underground and actually could make it even more dangerous for girls."
Instead, it's important to understand how these girls ended up in the business.
Japanese society has long considered this a situation in which the girls should take responsibility for their actions, but Nito says this attitude overlooks the girls' backgrounds and the fact that many have fallen outside mainstream social structures.
"They often don't receive the necessary help because they are just considered prostitutes or girls who are behaving badly," she said. "Unless this changes, girls will continue being lured into the JK business."
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