In an interview at the Foreign Ministry last month, Mr. Kono smiled impishly when asked how soon he might make a bid to lead the Liberal Democratic Party. “You never know,” he said. “Who predicted President Trump two years ago?”
Until being appointed to the cabinet last August, Mr. Kono, who speaks English fluently and left Tokyo’s prestigious Keio University to study at Georgetown University in Washington, was not usually on the list of potential heirs to Mr. Abe, given his sometimes more liberal views.
He is also the son of Yohei Kono, a previous foreign minister who, as chief cabinet secretary in 1993, issued a breakthrough apology to women from Korea and elsewhere who were forced to work as sex slaves in Japanese military brothels during World War II. Nationalists in the governing party have long resented the so-called Kono Statement, with some holding it against the son.
And unlike the typically somber political elite, Mr. Kono frequently shows a playful side.
Exhibiting a sweet tooth, he regularly postspictures of macarons served in foreign destinations. Of a photo of a box of M&M’s bearing Mr. Trump’s signature, Mr. Kono quipped, “Tastes the same.” Last month, he posted photos with Chinese officials and of a lunch menu in Beijing.
With an eye on persuading his own party to consider him for the top office, Mr. Kono has toned down some of his views and aligned himself with the administration.
As soon as he was appointed to the cabinet, Mr. Kono distanced himself from his father (to whom he famously donated a piece of his liver 16 years ago), reminding Foreign Ministry staff that “Yohei Kono and Taro Kono are completely different.”
Kunihiko Miyake, a former senior Japanese diplomat, said, “Taro Kono version 1.0 is now becoming version 2.0.”
In the interview last month, Mr. Kono declined to comment on his previous proposals to rid Japan of nuclear power. Instead, he offered an administration talking point: “The official Abe government nuclear policy is to reduce dependency on nuclear as much as possible,” he said.
Takao Toshikawa, editor of a political newsletter, Insideline, said of Mr. Kono: “Since he assumed an important ministerial position, I think he realized that the reality would not be changed only with an ideal.”
Still, the rebel peeks out. In a January speech in Abu Dhabi, Mr. Kono criticized Japan’s “lamentable” energy policy and exhorted his country to expand renewable energy.
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“Japan was way ahead in solar heat and photovoltaic before,” Mr. Kono said in the interview last month. “I think Japan was No. 1 and then we kind of fell behind.” He added, “If you don’t call it lamentable, I don’t know how to call it.”
Mr. Kono stays on the party’s message on key issues, including keeping up pressure on North Korea and adhering to a 2015 agreement with South Korea to resolve the dispute over the so-called comfort women who worked in military brothels.
“He’s been mostly very much toeing the Abe line,” said Kristi Govella, assistant professor of Asian Studies at the University of Hawaii at Manoa. “But there are some cases where he has been willing to say this is not the best policy.”
With a tweet, he can pierce the bubble of political pomposity. After giving an opening speech in Parliament last month, he called his performance “super high-strung.”
He takes some lumps on social media. After suggesting that the foreign minister should have a dedicated plane (he currently travels on commercial flights), he blocked several Twitter followers who criticized him for wanting to waste tax money.
While at Georgetown, he volunteered in a campaign for Alan Cranston, a Democratic senator from California, and interned for Richard Shelby, then a Democratic congressman from Alabama and now a Republican senator.
Senator Shelby described Mr. Kono as “probably stubborn, but he’s not stupid.”
“If he believes in something and he thinks he’s right,” Mr. Shelby said in a telephone interview, “he’ll stand his ground.”
Mr. Kono’s fluency in English makes him well suited to the role of foreign minister. At a meeting of world leaders in Manila last August, Mr. Kono effectively doubled the amount of time he was able to spend speaking with Rex Tillerson, the American secretary of state, because he did not need an interpreter.
He is the first Japanese foreign minister to visit Pakistan since 2009. He has taken an active interest in the Middle East and South Asia as the United States makes controversial decisions like moving the United States Embassy in Israel to Jerusalem and freezing security aid to Pakistan. In Jerusalem in December, Mr. Kono told Israeli and Palestinian leaders that the city’s status should be resolved through negotiations.
At home, he has called on Japan to open its borders to more immigration.
“We need to talk about immigration policy sooner because it’s a very psychological issue,” Mr. Kono said, acknowledging public wariness of foreigners. “I don’t think we can wait that long because we are losing our aging population fast,” he added.
Analysts point out that some of his views may not be so progressive. In the interview last month, he suggested that immigrants could be admitted if they demonstrate proficiency in Japanese, but in the past, Japan has used language requirements to bar immigrants.
To explain the tiny number of refugees in Japan, Mr. Kono repeated the government’s line that most asylum seekers are “falsely applying” and just want to work in Japan.
As for his political ambitions, commentators say one challenge will be persuading the right-leaning Liberal Democrats to choose him.
“He must be dreaming of a version 3.0 in the future,” said Mr. Miyake, the former diplomat. “But to get to version 3.0 is much more difficult than getting from 1.0 to 2.0.”