Tokyo Report | Politics | East Asia

The Awakening of Koizumi Shinjiro

How a defense portfolio transformed Japan’s most underestimated politician. 

Japanese Minister of Defense Koizumi Shinjiro holds a joint press conference with U.S. Secretary of Defense Pete Hegseth (not pictured) at the Japanese Ministry of Defense in Tokyo, Japan, Oct. 29, 2025.

The race to become Japan’s next prime minister in 2025 – the Liberal Democratic Party’s presidential race – was Koizumi Shinjiro’s to lose. Polls and pre-election gatherings among Diet members indicated that he was the overwhelming favorite to secure the support of Diet members and outperform Takaichi Sanae, who remained popular among the grassroots conservative base of the Liberal Democratic Party. 

Before the LDP presidential election, Koizumi’s patron, Suga Yoshihide, had begun reaching out to Nippon Ishin no Kai to coordinate a new coalition that would provide the Koizumi administration with a working majority in both houses of the Diet. There were even reports that members of his campaign team were holding a ”celebratory party” the night before the ultimate result was to be called, treating Koizumi’s victory as an absolute certainty.

However, things did not turn out as expected for Koizumi. He significantly underperformed among rank-and-file members and was defeated by Takaichi, the most popular candidate among the LDP’s core supporters. Takaichi convinced Diet members that she could turn the tide for the party and reclaim its conservative edge – which had seemed to be waning due to a right-wing revolt against a party perceived to be distancing itself from them. 

One immediate cause of this turn of events was the scandal surrounding the Koizumi campaign team’s dissemination of pro-Koizumi comments – and ones disparaging his opponents – during online streaming, which dented his authenticity as a candidate. But the critical issue that thwarted his victory not only in 2025 but also in 2024, when he first sought the premiership, was his perceived inexperience. Koizumi’s reliance on prepared remarks during public debates likely highlighted concerns among party members that he needed more seasoning to be a trustworthy leader in a time of trial. The surge of fellow candidate Hayashi Yoshimasa – an experienced administrator who finished third in the race, behind Takaichi and Koizumi respectively – attested to the importance of experience as a deciding factor in selecting a party leader within the LDP.

Despite coming in second place, Koizumi’s loss was not entirely a step back. In fact, his appointment as minister of defense – a high-profile position and especially important in a Takaichi administration where defense policy is a priority – seems to have changed his persona overnight. 

Since Koizumi landed in his new role, he – and the Ministry of Defense as a whole – has notably increased public outreach through various media – a goal Koizumi set out when he assumed the job. Koizumi’s appearances in long-form online programs, and the public announcements of foreign military activities surrounding Japan, are part of his efforts to increase transparency into the ministry’s work, and also raise awareness among the public of “the most severe and complex security environment since the end of World War II” that Japan faces. These efforts have given a spotlight to Koizumi as Takaichi’s spokesperson for her resolute defense policy – and, in the process, overhauled public perceptions of Koizumi.

Even his political opponents – especially those more attuned to online discourse – have picked up on this shift in mood. Shinba Kazuya, the secretary-general of the Democratic Party for the People, whose daily press briefings have become popular online content in their own right, shared his observation that he sensed Koizumi was an “awakened man,” and praised his expertise on the Japanese Maritime Self-Defense Force, which is based in Koizumi’s electoral constituency. Hyakuta Naoki, the head of the Conservative Party of Japan, who has been a conservative........

© The Diplomat