The notable thing about the title Predator: The Secret Scandal of J-Pop (BBC2, Tuesday) is that the scandal it refers to is only a secret outside of Japan.

Inside the country, pretty much everybody, young or old, knows the name Johnny Kitagawa. And why wouldn’t they? The man was a showbusiness legend, a bona fide national treasure.​

Kitagawa, who died in 2019 at the age of 87, was the architect of the country’s idol culture. For decades, he and his talent agency Johnny & Associates, which later expanded to include a record company, has been a production line that smoothly turns out one chart-topping, record-breaking, arena-filling J-Pop boyband after another.

All over Tokyo, the fresh young faces of “the Johnnies”, as the bands are collectively and colloquially known, beam from hoardings, video screens and store window displays, advertising everything from contact lenses to real estate.

Johnny & Associates jealously guards the images of its manufactured stars. Kitagawa was similarly protective of his own image. Very few photos of him exist. He almost never gave interviews or made public appearances. Yet when he died, a nation mourned. His funeral received the kind of coverage usually reserved for monarchs. Japanese celebrities turned out in force. The country’s then prime minister, Shinzo Abe, sent a message of condolence.

Pretty much everyone in Japan knows something else about Johnny Katagawa: that he was a paedophile who lured boys, some as young as 12, to his agency with the promise of pop stardom and then sexually abused them.

But as journalist Mobeen Azhar discovered — to his bewilderment and horror — in this riveting, shocking documentary, Japan seems to be in the grip of mass denial about its most famous paedophile, or else have chosen to ignore the truth.

Two people who couldn’t ignore it were the journalists from the respected weekly news magazine Shūkan Bunshun Azhar spoke to. In 1999, they were approached by a boy who told them he’d joined the Kitagawa agency as a 16-year-old schoolboy and was sexually abused by Johnny.

Other boys came forward. Their horribly graphic accounts chimed. Kitagawa would bring them to one of his homes, where they were billeted with other boys in a room called “the dormitory”. Every night, he came in and preyed on one of them.

Usually, this was preceded by him insisting they take a bath. He removed their clothes and bathed them himself. The understanding among the more experienced boys was that you had to put up with this if you wanted to be a J-Pop star. Some made the grade; most didn’t and returned to their normal lives.

When the article appeared, it was ignored by the rest of the Japanese media. No newspaper or radio station followed it up or even mentioned it. The suspicion was they were afraid to jeopardise their profitable relationship with Johnny & Associates. Kitagawa sued Shūkan Bunshun for libel. The trial, a civil one, lasted four years. The Japanese High Court accepted that nine of the 10 allegations that Kitagawa had sexually abused the boys were true. Unbelievably, there was no follow-up criminal investigation. Whenever Azhar asked about Kitagawa, he hit a wall of silence. Young J-Pop fans buying posters in a shop refused to talk to him. The police blanked him. A fellow journalist wouldn’t let him see the meagre few photos and video clips his organisation has of Kitagawa.

Azhar managed to find a few of Kitagawa’s former boys who were willing to talk. One, Hiyashi (not his real name) broke down while recalling Kitagawa anally raping him. But others, such as Ryu, seemed reluctant to condemn Kitagawa.

“I don’t dislike Johnny,” he said. “I love him. Johnny was really a wonderful person and I owe a lot to him. I still think that we were treated with great love.”

Near the end of the film, having been batted away with a bland corporate statement from the seemingly untouchable Johnny & Associates, Azhar was angry and appalled. If only the Japanese media could summon those emotions.