Japan-Korea relations are like a roller coaster. And the factor that usually proves most important is the political commitment and strength of the leaders in Tokyo and Seoul. Chun Doo Hwan and Nakasone Yasuhiro made progress in the 1980s when both were at the top of their popularity. Kim Dae Jung and Obuchi Keizo issued an historic bilateral joint statement on future relations in 1998 when they both enjoyed the strongest public support of their tenures. Strong leaders sometimes choose not to improve relations — which was the case when Abe Shinzo and Moon Jae-in presided over a negative period in Japan-Korea relations despite having won major elections at home. And international factors such as the pressure of Soviet Russia or Xi Jinping’s China or sometimes American prodding can also be important. But real progress in Japan-Korea relations ultimately comes down to whether the two countries’ leaders have the intent and the political wherewithal to overcome domestic opposition and put bilateral relations on an even keel.

President Yoon Suk Yeol and Prime Minister Fumio Kishida are the most recent leaders to demonstrate that determination and political acumen. Though Xi Jinping’s coercive diplomacy and Joe Biden’s July 2023 Camp David trilateral summit certainly helped, it was Kishida and Yoon who saw the historic opportunity for their countries and seized it.

So what does it mean for Japan-Korea relations now that Japanese Prime Minister Fumio Kishida's political position is collapsing around him? Plagued by funding scandals, Kishida’s support rate recently hit a new a new low of just 20 per cent in public opinion polls. The speculation in Nagata-cho (Tokyo’s political district) is not whether Kishida will survive, but who will replace him as president of the Liberal Democratic Party (LDP) and thus prime minister in the party convention in September. Will the new momentum behind Japan-Korea relations now also collapse — as has happened so often in post-war history?

I do not believe so.

First, President Yoon has seen his own political fortunes rebound in recent months. He now enjoys almost 40 per cent in the polls and one reason for his success is that the public supports his foreign policy, including improved relations with Japan. The Korean public knows that under Moon their country was too isolated from other democracies around the world and that putting Korea back on the global map meant repairing relations with Japan. We will see what happens with April 10 parliamentary elections, but Yoon is in a strong position to help a new Japanese prime minister keep up Kishida’s momentum, whoever it is.

Second, there is now a strong consensus in Tokyo that strong relations with Korea are essential for Japan’s own regional and global position. During the Park and Moon years, I found Japanese strategic experts divided on whether Korea really mattered to Japan when domestic Korean politics were so difficult and there was so much more momentum for Japan in relations with the Quad countries like India and Australia. That dynamic has completely changed. In a soon-to-be published survey of security experts in Tokyo conducted by the Center for Strategic and International Studies (CSIS) in Washington and the U.S. Studies Center in Sydney, over 90 per cent of Japanese strategic experts agreed that continuing to improve relations with Korea was essential for Japan’s own security.

And third, Kishida’s most likely successors have no reason to interrupt the progress being made with Korea — which is an important change from the past. My own list of post-Kishida prime ministers in order of likelihood would go like this:

• Yoko Kamikawa, the current foreign minister, seems poised to be Japan’s first woman prime minister. Harvard-educated and considered a tough law-and-order justice minister in her previous role, there is every reason to believe that she would get on famously with President Yoon. She has the strongest support behind the scenes with strong factional leaders in the LDP, though her public standing is not that much higher than the other contenders.

• Motegi Toshimitsu, the LDP secretary general, was the minister of economy, trade, and industry. Another Harvard grad, Motegi has internationalist instincts and would be inclined to continue Kishida’s Korea policy. He has a prickly personality, though, and his poll numbers and popularity with the LDP are well below the quality of his resume.

• Koizumi Shinjiro, son of former Prime Minister Koizumi Junichiro and a former researcher at the Center for Strategic and International Studies under this author, is very popular with younger voters but considered by the elders of the LDP to be still too young for the top job. He has largely focused on domestic issues since returning from Washington and joining the Diet, but I have seen him in action and his internationalism is well entrenched.

• Kono Taro, the former foreign and defense minister, is extremely popular in the United States and especially at his alma mater Georgetown University in Washington, D.C. He has struggled in his current role overseeing the digital agency and he threatens older politicians who have jumped on these policy problems to slow him down. He was tough on Korea as Foreign Minister (like Kishida when he had that role) but this was primarily because he was frustrated with the Moon government’s reversal of the agreements struck between Abe and Park Geun-hye. He is instinctively an internationalist thinker who’s father Kono Yohei went to great lengths to strengthen ties with Korea and he could be expected to do the same.

• Sanae Takaichi is the most hawkish and nationalistic of the possible successors to Kishida and might be one to worry Seoul. However, her path to the party leadership seems narrow and political observers have noted that she has very few colleagues joining her study group in the Diet, a sign of weak support in the party. Even if she did become head of the party and Japan’s first female prime minister through backroom factional arrangements, she may well prove a supporter of furthering Japan-Korea ties, focusing her hawkishness on China instead.

• Ishiba Shigeru is somewhat popular with the public, but he has many enemies in the LDP. He would need Kono and Koizumi to back him, but he now represents an older generation and that is not their game. Ishiba’s policy positions are quirky and driven by whim rather than ideology — which makes officials nervous — but there is no reason to suspect he would reverse Kishida’s Korea policy, even if he would reverse many other initiatives.

Of course, it is possible that Kishida survives, but one thing comes through reviewing his possible successors — nobody is going to run against Korea. It appears that for now Korea-Japan relations have enough momentum to withstand political turbulence at home in either country.