Koike, 64, is a former television journalist fluent in English and Arabic. She’s known for breaking the glass ceiling several times over, being the first woman to serve as defense minister -- albeit briefly -- and to contest the leadership of the ruling Liberal Democratic Party. She frequently publishes essays on international issues, including one referring to Donald Trump’s election campaign as "loutish."
In Sunday’s gubernatorial election, she beat 20 candidates including Hiroya Masuda, a former regional governor backed by Prime Minister Shinzo Abe, and Shuntaro Torigoe, a journalist. She made extensive use of social media, on which she encouraged supporters to wear her signature green.
Chief Cabinet Secretary Yoshihide Suga said on Monday it was "extremely regrettable" that the LDP’s candidate had been defeated, but added that the national government must work with the Tokyo assembly for the good of the people.
Koike faces multiple challenges in managing a city with a population of more than 13 million and a budget the size of Sweden’s. After a series of scandals and soaring budget costs that led to the design for the flagship stadium being scrapped, she must restore faith in Tokyo’s plans for the hosting of the Olympics.
This means she’ll have to work closely with Abe despite his campaigning against her. The pair will be together in Rio de Janeiro for the closing ceremony later this month, according to media reports.
"This immediately makes Koike visible in a way that no woman has been before in Japanese politics," said Tobias Harris, an analyst with Teneo Intelligence in Washington. "A Tokyo governor is a major national figure, all the more so due to 2020."
Even so, Harris said Koike’s election won’t necessarily help women advance into national leadership. While Abe has promoted a longstanding target of having women in30 percent of supervisory positions in all fields by 2020, he is far from reaching that goal in his own cabinet, where three of the 20 current members are female.
While 20 percent of the Tokyo assembly is female, an LDP assemblyman was forced to apologize after sexist heckles during a speech by a young assemblywoman two years ago. Koike’s predecessor, Yoichi Masuzoe, was criticized for saying those who menstruate are not fit to lead.
"When she ran for party leader in 2008, it made me realize that a woman can put herself forward to be prime minister, and that was encouraging," said Reiko Ueda, a Tokyo assemblywoman who campaigned for Koike.
As environment minister, Koike became known for promoting casual dress in Japan’s humid summers to save power by reducing the need for air conditioning. Starting with politicians and bureaucrats, the "Cool Biz" custom eventually became established in Japan’s conservative business community.
She resigned from parliament to run for the governorship.
Not Like Ishihara
While the position of governor is local in focus, previous incumbents have been known for their involvement in a broader sphere. Then-governor Shintaro Ishihara’s 2012 campaign to have the Tokyo government buy East China Sea islands disputed with China prompted the national government to purchase them, sparking the worst bilateral crisis in decades.
Koike has told reporters she has no plans to do anything "like Mr. Ishihara."
On the campaign trail, Koike pledged more transparency in government, a cut in her own salary, and a review of the budget for the Olympics. She vowed to provide more care facilities for children and the elderly and to take advantage of Tokyo’s status as a special economic zone, where lighter regulation allows for new initiatives.
Former governor Masuzoe stepped down in June when the city assembly threatened to pass a no-confidence motion against him over alleged misuse of political funds and official perks. His predecessor Naoki Inose resigned in 2013 amid questions over a 50 million yen ($490,000) loan from a hospital operator.
"I may have attracted interest for being a woman, but what I think most people want from me is a new kind of politics in the capital," Koike told reporters at her campaign office after claiming victory.