Karoshi became widely recognized as a phenomenon in the late 1980s, as stories of blue-collar employees keeling over at work appeared to expose a sinister side to Japan’s postwar economic miracle. Over the years, cases of karoshi have been reported among white-collar executives, automotive engineers and immigrant trainees.

In a 2016 government report on karoshi, nearly a quarter of companies surveyed said that some employees were working more than 80 hours of overtime a month. Months later, the president of the advertising agency Dentsu resigned after an outcry over the 2015 death of an employee, Matsuri Takahashi, 24, who jumped from the roof of an employee dormitory.

Like Ms. Takahashi, Ms. Sado was a young woman making her way in a blue-chip organization. Her employer is considered one of the most prestigious companies in Japan, a country where exhaustion is often seen as a sign of diligence.

A 2014 government investigation found that Ms. Sado’s death was a direct result of her work life.

“She was under circumstances that she could not secure enough days off due to responsibilities that required her to stay up very late,” the labor office in the Shibuya section of Tokyo said in a statement to the Asahi Shimbun newspaper. The office described her as being “in a state of accumulated fatigue and chronic sleep deprivation” at the time of her death.

The broadcaster said it had delayed revealing details about Ms. Sado’s death out of respect for her family and timed the release to coincide with planned workplace changes.