The president of Japan's biggest boyband agency admitted on Thursday that its late founder sexually abused young aspiring stars, decades after the allegations against him first emerged.

Johnny Kitagawa died of a stroke aged 87 in 2019, having engineered the birth of J-pop mega-groups including SMAP, TOKIO and Arashi that amassed adoring fans across Asia.

Allegations of abuse surfaced in Japanese media in 1999 but it was not until this year that they ignited full-on soul-searching, following a BBC documentary and denunciations by victims. 

"Both the agency itself and I myself as a person recognise that sex abuse by Johnny Kitagawa took place," said Julie Fujishima, a niece of the accused music mogul who died in 2019.

"I apologise to his victims from the bottom of my heart," she told a packed news conference in Tokyo while announcing she was stepping down as head of Johnny & Associates "to take responsibility".

"I take seriously what happened."

Fujishima, who said she had stepped down on Tuesday, named singer and actor Noriyuki Higashiyama, a veteran member of the talent agency, as her successor. 

"It will take an enormous amount of time before we can regain trust," Higashiyama said.

"I will stake the rest of my life on addressing this problem."

Fujishima said she will remain in the agency's leadership to help "compensate" victims.

- Defamation -

Before his death, Kitagawa had successfully sued for defamation over the claims, although the verdict was partially overturned on appeal.

He was never criminally charged.

A panel of experts last month released the results of its first, in-depth probe into the allegations against Kitagawa, concluding that his abuse went as far back as the 1950s, even before the company was founded.

Over the years, aspiring boyband idols collectively dubbed "Johnny's Jrs" sought his tutelage, and the panel estimated that at least "a few hundred" of them had been victimised.

The report also quoted former recruits alleging in graphic detail how Kitagawa would perform oral sex on them, fondle them in their genitals or force his way into their beds at night.

The panel said Fujishima, who was named Kitagawa's successor after his death, had been "remiss" in her duties because she failed to probe the allegations despite her knowledge of them. 

Her attitude perpetuated the leadership's tendency to look the other way, the report said. 

Fujishima, for her part, offered an apology in May but denied she had known about her uncle's predatory history. 

She chalked her ignorance up to what she framed as the extremely opaque, family-run nature of the boyband empire. 

"We do not believe there was no problem," she said in May, expressing her regret that she had let herself grow inured to the "abnormalness" of the agency's inner workings.  

Her apology came after Japanese-Brazilian singer Kauan Okamoto spoke publicly of his experience of being sexually assaulted repeatedly by Kitagawa. 

tmo/stu/qan