It began as a scoop in a weekly tabloid: the allegation that a middle-aged former boy-band star turned top television host had paid hush money to a woman for unspecified wrongdoing.

Other articles followed, asserting that it was a case of sexual assault, and stirring a wave of public outrage not only toward the ex-singer but also his employer, a major TV broadcaster, for how it handled the situation.

On Thursday, the man at the center of the controversy announced his retirement, but the episode had already turned into a moment of reckoning. An international investor has criticized the company, Tokyo-based Fuji Television, and Japan’s biggest corporate advertisers have lined up to boycott it. Some 75 companies, including Toyota, SoftBank and the local operator of McDonald’s, have pulled ads and sponsorships.

Not a single commercial now appears on the station’s programming; ad spots are now filled with unpaid public service announcements. Tens of millions of dollars in revenue is at stake as indignant C.E.O.s have called on Fuji TV to address the issue.

“We will cease placing advertisements with the company until a thorough investigation is conducted, the facts are clarified, and appropriate action is taken,” Takeshi Minakata, president of the drink maker Kirin, said in a statement, which added that the company was acting “based on our human rights policy.”

Experts say the anger reveals a new intolerance for sexual misconduct set in motion by an earlier scandal. Two years ago, it emerged that the founder of a top talent agency had sexually abused young men for decades. He died in 2019 without ever facing any charges, and corporate sponsors were accused of having ignored the wrongdoing at the agency, Johnny & Associates.