Over the course of a month, she clocked 159 hours of overtime. She rarely took weekends off. She worked until midnight nearly every night. On her birthday, June 26, she emailed her parents, who thought she sounded weak.
Not quite a month later, just days after the second election, she died of congestive heart failure. She was 31.
The case — the latest high-profile example of karoshi, or “death from overwork” — came to light only after the broadcaster, NHK, announced it this week.
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 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.
“We decided to disclose her death to all of our employees and to the public to share the company’s resolve to prevent a recurrence and follow through with reforms,” NHK said.
Ryoichi Ueda, the president of NHK, said that Ms. Sado’s parents “hoped we would take utmost efforts so that another such case won’t happen again.”
But Ms. Sado’s parents criticized NHK’s response as inadequate. In a statement published by the Asahi Shimbun on Thursday, they said they feared that her death would be forgotten and “wondered if the company would keep hiding it, or why the union kept silent.”
Her parents also asked why the company had not limited their daughter’s working hours.
“It is an abnormal work situation to work almost every day on Saturday and Sunday, working until late at night every day, so we cannot understand why such a situation was overlooked,” their statement said.
Although they did not immediately publicize their daughter’s death, they said that Ms. Takahashi’s case had spurred them to publicly discuss it.
They also criticized NHK for not disseminating news of their daughter’s death throughout the company. They said that other employees — even journalists who had reported on other cases of karoshi — did not know that one of their colleagues had died from the condition.
Karoshi, which has included the burden of entertaining clients or bosses in some industries, has long prompted calls for legislation.
The Japan Institute for Labor Policy and Training, in a white paper released last year on the prevention of karoshi, noted that the “undeniable problems in Japan’s work environment” were especially detrimental to regular employees under age 35.
National guidelines use a threshold of 100 hours of overtime in a month — or an average of 80 hours of monthly overtime in a six-month period — to determine whether a worker is at risk of physical or mental harm. Those guidelines were put forward by a government panel in April, but critics say that more is needed.
In February, the Japanese government and the Keidanren, Japan’s largest business group, introduced an effort dubbed “Premium Friday” that encouraged companies to allow workers to leave the office at 3 p.m. on the last Friday of the month.
Only a fraction of companies are participating.