Japan's vaccine tsar and a low-key moderate are among the possible replacements for Prime Minister Yoshihide Suga, who said Friday he will not run in his ruling party's leadership vote.
Only one Liberal Democratic Party (LDP) member has so far announced their candidacy for September 29 vote, with the winner obliged to call a general election by late October.
Here, AFP profiles some potential candidates:
Fumio Kishida, dovish ex-minister
Fumio Kishida, 64, is the only declared candidate and has already pledged to spend big if elected, promising a new stimulus package to counter the effects of the pandemic on the world's third-largest economy.
The soft-spoken politician is seen as "moderate and capable", making him a top pick for the premiership, according to Tomoaki Iwai, a politics professor at Nihon University.
Although the ex-foreign minister is head of an LDP faction known for its dovish stance, his low-key presence and alleged lack of charisma could hamper his chances.
Elected from Hiroshima, Kishida worked to invite then-US president Barack Obama for a historic 2016 visit to the city which was devastated by an atomic bomb.
He also helped cement a deal between Japan and South Korea that was meant to end a long-running dispute over the use of sex slaves during Japan's occupation.
Taro Kono, vaccine tsar
Former defence minister Taro Kono has overseen Japan's vaccine rollout, which began slowly but has picked up speed, with just under half the population now fully inoculated.
The 58-year-old was once considered an ambitious and independent-minded political reformer, but has toned down his rhetoric in recent years.
Currently minister for administrative affairs, Kono -- a fluent English speaker and keen Twitter user -- served as foreign minister between 2017-19.
He travelled extensively as Japan's top diplomat, but also oversaw the deterioration of ties with South Korea over unresolved wartime disputes.
In recent years, he has largely avoided discussing his passionate opposition to nuclear power, given the government's official support.
Shigeru Ishiba, popular military geek
Former defence minister Shigeru Ishiba, 64, is considered a military geek but is also a self-confessed fan of 1970s pop music.
The former banker is the scion of a political family and is seen as popular with the public, and a strong orator with significant experience.
Seen as a hawk who wants to strengthen the role of Japan's Self-Defense Forces in the pacifist constitution, Ishiba has even mused about whether the country should reconsider its policy forbidding nuclear weapons on its soil.
He has served in several cabinet posts, but he may struggle to win votes from his fellow ruling party lawmakers, partly because he once left the LDP.
In June, Ishiba courted controversy when he said the work of a far-right, Covid-denier cartoonist could be useful for the government's virus response.
Sanae Takaichi, divisive hawk
Sanae Takaichi, one of Japan's few prominent female politicians, is seen as a hard-right nationalist and has been forced to apologise for several gaffes over the years.
She is a regular visitor to Tokyo's controversial Yasukuni shrine, which honours war dead including war criminals, enraging South Korea and China.
A divisive figure within the party, the 60-year-old most recently served as minister for communications and internal affairs, vowing to tackle cyberbullying after the death of a reality star.
During a previous stint as interior minister, she threatened to cut off TV news stations over perceived unfriendly coverage.
Hakubun Shimomura, ex-education minister
LDP policy chief Hakubun Shimomura had said he wouldn't challenge Suga after the prime minister reportedly asked him to leave his powerful party post if decided to run.
But with Suga no longer in the picture, the 67-year-old former education minister could throw his hat in the ring.
Shimomura has worked to plan Japan's Covid-19 countermeasures, with large swathes of the country under a virus state of emergency for most of this year.
Having lost his own father when he was nine, he faced financial hardship growing up but won scholarships for his own education.