An independent probe into one of Japan's top talent agencies has urged its president to step down. It's over sexual abuse allegations involving the founder of Johnny & Associates spanning decades.

Johnny Kitagawa was once hailed as the biggest producer in male J-pop. He even held a Guinness World Record for the most number one hit singles produced by an individual.

Kitagawa died in 2019, and several men who worked with him while underage have accused him of sexual misconduct.

On Tuesday, a team of legal and sexual abuse experts enlisted by the agency submitted a report into the allegations.

The expert team's chairperson, Hayashi Makoto, said, "Our special team recognized that Johnny sexually assaulted a number of minors, including 'Johnny's Junior' trainees, at locations including his home, training camps, and hotels while on tour."

The team interviewed 23 alleged victims. They included former backup dancers known as "Johnny's Juniors," who were mostly teenagers hoping to make their break in the music business.

The probe concluded that Kitagawa began sexually abusing boys in the 1950s, and committed assaults into the mid-2010s.

It implicated Johnny's older sister, Mary Kitagawa, of failing to take action, as well as trying to cover up her brother's abuse of underage boys. Mary held a managing role in the agency.

Her daughter, Julie K. Fujishima, is Johnny's current president but the expert team says she should not remain in that role.

Hayashi said, "We think Johnny & Associates needs to replace the person at the top of the organization in order to make a fresh start. We are demanding that Julie resign as representative director."

The probe also recommends the agency acknowledge and apologize for its founders' abuses, and begin talks with the victims. It also suggests the firm immediately set up a program toward compensation.

One of the survivors said the report was comprehensive, and added he agrees with its call for apologies and relief measures.

The deputy head of a victims' group, Ishimaru Shimon, said, "Even if the president steps down, she should not be absolved of blame. As the head of the company, she has a social and moral responsibility."

Johnny & Associates says it takes the report very seriously.

Revelations around the agency's founder have prompted international scrutiny, including a UN investigation.

Japan's government has promised measures to combat the abuse of young male entertainers, including a hotline for male sexual assault victims.