TOKYO (Reuters) - “At that moment, I understood what it means to feel like I’d rather die,” wrote a young Japanese woman, recalling the trauma she suffered as a pre-teen, over having sex with a man to earn funds to repay what she thought was a debt.

The testimonial was part of an exhibit, including photos and artwork, in the Japanese capital that sheds light on an underground industry known as “enjo kosai”, or compensated dating, where men pay girls for dates that often lead to sex.

Japanese men’s fascination with high-school girls fuels demand for such services, and exhibit organizer Yumeno Nito said many people have the wrong idea about the girls themselves.

The mere use of the word “compensated” implies the girls seek fun and money, rather than being victims of sexual trafficking, said Nito, who heads a non-profit organization, Colabo, that provides support to such young women.

“There is a notion the girls are guilty because they willingly sold their bodies,” she said, adding that the phrase “compensated dating” was unique to Japan.

The age of consent for women is 13 years in Japan, although there can be exceptions.

It is the girls’ youthfulness, poverty and naivety that make them vulnerable to abuse, Nito said.

“I started so I could escape mundane daily life,” wrote another young woman, who lied about her age to get a job accompanying older men on walks, or “JK osanpo”, as it is known. The job soon escalated into touching and kissing, wrote the woman, who later went to work at a brothel for higher pay.

“If there are people who are thinking of entering the business, I would want them to stop immediately,” she added.

The U.S. State Department cited “enjo kosai” as a worrying trend in its 2016 report on human trafficking, based on research in which it collaborated with Colabo.

“Sophisticated and organized prostitution networks target vulnerable Japanese women and girls in public areas such as subways, popular youth hangouts, schools, and online; some of these women and girls become trafficking victims,” it said.

The United Nations, in a separate report, highlighted the problem, the full scope of which it said was hard to grasp because of legal ambiguities.

Although firm data is hard to come by, the phenomenon also worries Japanese police.

Educators and others “need to be fully aware of the harm and danger of ‘JK business’ and guide and advise youth so they do not become involved”, Tokyo’s Metropolitan Police Department said this year in a report,

In 2014, responding to criticism that it was lax in protecting minors from sexual exploitation, Japan revised the law to ban possession of child pornography, partly in an effort to clean up its image ahead of the 2020 Tokyo Olympics.

Still, critics say the ban is limited to depictions of real children. Graphic images in manga and anime are largely exempt.

“I feel the situation is improving,” Nito said, referring to growing awareness of the problem. “But the crimes are still not being reined in.”