The news traveled fast in Yawata, a spiritual oasis of 68,000 people in western Japan known for its traditional tea culture and cherry blossoms. Shoko Kawata, the city’s mayor, was pregnant with her first child — and she was planning to take maternity leave, the first mayor in Japan to do so.

Many residents of Yawata celebrated Ms. Kawata, 35, and her decision, which she announced in May. They offered gifts like crocheted baby shoes and auspicious ceremonial rocks. But in Japan’s patriarchal society, some people — especially men — responded with anger, calling her irresponsible, and accusing her of placing her personal life above her constituents.

“I somehow realized for the first time just how much discrimination still exists,” Ms. Kawata, who is six months pregnant, said in an interview this past week at City Hall, inside a room lined with portraits of her male predecessors.

Ms. Kawata’s decision has prompted a national debate about the hurdles that working women still face — on the factory floor, in corporate suites and in government. Discrimination against young mothers is still so common that there is a Japanese word for it: matahara, or maternity harassment. Some women feel pressure to avoid taking extended maternity leave, worried their careers might suffer.

Despite the history-making election last year of Sanae Takaichi as Japan’s first female prime minister, women are still scarce in Japan’s government. That is especially true at the local level. As of last year, less than 4 percent of 1,740 municipal leaders were women.

Ms. Kawata has been hailed as a trailblazer by some officials, scholars and activists, who say she is helping normalize the idea of maternity leave.

Kyoko Morisawa, the mayor of Shinagawa City, a part of Tokyo, said it was important for Japan to have more young mothers like Ms. Kawata in public life, especially given the rapidly declining population.

“We should do more to support child-raising as a society,” said Ms. Morisawa, a mother. “Taking leave should not be news.”

Ms. Kawata, who previously worked as a social worker and political aide, is accustomed to challenging convention.

In 2023, when she was 33, she became the first woman to be elected as Yawata’s mayor, and the youngest woman ever elected mayor in Japan, succeeding a 71-year-old politician with promises to expand medical care for children and promote tourism.

When she learned she was pregnant this year, she decided, after discussing with her staff, to take about two months before the birth — expected in mid-September — and two months after. She arranged for a deputy to manage day-to-day business while she is away, though she will remain involved in major decisions.

As word of her pregnancy spread in the national media, she held a news conference to explain her decision.

“Systems can be changed, but people cannot,” she told reporters. “I cannot become a man.”

The announcement caused a stir in Yawata, a town near Kyoto city that is dotted with Shinto shrines and Buddhist temples. City Hall received about 90 messages in support of Ms. Kawata’s decision, and 70 opposed.

A heated debate erupted online. One of the loudest voices was Toshio Tamogami, a retired general and nationalist politician, who wrote on X that he felt “a great sense of discomfort about someone in public office taking such a long vacation.”

In an interview, Mr. Tamogami said he felt that women who plan to have children or take maternity leave should avoid running for office.

“Unlike people in ordinary jobs, a mayor is, so to speak, irreplaceable,” he said. “To say, ‘It’s my right, so I’m running regardless’ — I feel it would be better if they refrained from doing so.”

Ms. Kawata, who has taken a break from social media because of the backlash, said it was regrettable to be “fiercely attacked” by Mr. Tamogami and others.

Many people have come to Ms. Kawata’s defense, saying Japan would benefit from more women in politics.

“Japan needs to create an environment in which people can take that leave as a matter of course,” said an editorial in the national Mainichi newspaper.

In Yawata, residents said they were proud that their mayor was modeling the importance of starting a family. Some have encouraged her to have even more children.

As she walked outside City Hall with a friend on a recent day, Toshiko Nakamura, 81, recalled that when she gave birth to her own children, maternity leave was rare. She said Ms. Kawata was helping set an example.

“Japan has a low birthrate, so raising children while simultaneously leading a public office is difficult, but there are many people who can help,” she said. “I hope they’ll raise their hands and offer that help.”

Inside her office, Ms. Kawata said her aim was to “create a society where talented individuals — regardless of gender — can demonstrate their abilities in high-level positions without having to sacrifice their family life.”

She said she hoped she might inspire more women to enter politics.

“It won’t be easy, but that is something we should aim for,” she said. “Policymaking will be better than ever before.”