Magazine journalist Ryutaro Nakamura had heard rumours about a top music producer in Japan sexually abusing boys and teenagers.

His journalism instincts told him to dig. And they were right.

One day, he found the proof he was looking for.

WARNING: This story includes details of sexual assault and rape, which some readers may find distressing.

Three men agreed to go on the record and recount how they were raped and sexually abused as teenagers by industry heavyweight Johnny Kitagawa.

"When [one victim] told me about what had happened, his voice would tremble and he would cry," Nakamura told the ABC.

"I felt shocked and apologetic at the same time.

Kitagawa was a giant of Japan's powerful J-pop industry, credited with inventing the very style of boy band the country is famous for.

Over his five-decade career at the helm of production agency Johnny & Associates, he created Japan's biggest pop stars, perhaps most notably the boy group SMAP.

His celebrities didn't just create hit records, they infiltrated every corner of mainstream media, from television shows to advertisement billboards, guaranteeing high ratings and interest.

But away from the bright lights of the entertainment industry, Kitagawa was luring starry-eyed boys and teenagers to his home, where he would sexually abuse and rape them, according to multiple victim statements proven in court and eyewitness accounts.

In 1999, Nakamura and his colleagues published a series of reports in Weekly Bunshun magazine that detailed multiple allegations of boys being raped by Kitagawa.

The journalist was sure the revelations would destroy Kitagawa's career and change the music industry for the better.

But instead, it was met with silence.

"I approached my various media friends and colleagues, and asked them to follow up on our story," Nakamura said.

"I told them that serious human rights issues should be taken up, but they were reluctant to do so.

"I was disappointed at every turn."

How 'Johnny's Boys' were allegedly groomed in 'the dormitory'

The images of Johnny Kitagawa and his proteges were meticulously curated and controlled, and Japanese media were all too happy to accommodate.

Kitagawa's agency, after all, had the best stars.

Very few photographs were ever published of Kitagawa himself, as the media would agree with his demands of staying out of the spotlight.

Japan's public broadcaster, NHK, once broadcast an interview with Kitagawa that was shot from the neck down. 

Unlike other agencies, Johnny & Associates only dealt with boy bands, not girls or women.

To become a "Johnny's Boy", children and teenagers were selected through an audition process.

Those who impressed Johnny Kitagawa could then rise through the ranks from a background dancer to a fully fledged pop idol.

Nakamura said the boys would often stay at Kitagawa's home, called the "dormitory", without other parental supervision. He said this was where Johnny would take advantage, offering the children alcohol and cigarettes.

After the series of reports in 1999, Kitagawa sued the magazine for defamation.

But the lengthy court battle, rather than quashing the reports, vindicated the journalists.

Tokyo's High Court found the claims of sexual abuse reported in the Weekly Bunshun were correct.

And yet, police did not file any charges. The press also ignored the matter.

Nakamura was flabbergasted.

"I was really shocked," he said.

"I wondered how such a thing could happen in a civilised country."

The 'elephant in the room' after a media giant's death

The case of Johnny Kitagawa has drawn comparisons with that of other high-profile celebrities found to have abused their power, including Britain's Jimmy Savile, Australian entertainer Rolf Harris, and Hollywood producer Harvey Weinstein.