The straight-talking, social media-savvy minister for vaccines is the front-runner in the race.
He is popular among the young and has a Twitter following of 2.4 million.
Backed by PM Suga, he belongs to the faction led by Finance Minister Taro Aso.
The former foreign minister represents mainstream views on most issues, including a strong alliance with the US.
In 2016, he helped realise a historic visit by former US president Barack Obama to Hiroshima, his constituency.
He is committed to nuclear disarmament and has called it "my life's work".
The former internal affairs minister is known for her ultra-conservative views.
She made regular visits to the Yasukuni Shrine and strongly opposes apologies for Japan's wartime past.
A heavy metal fan and a motorbike enthusiast, she favours traditional gender roles and a paternalistic family system.
The former gender equality minister campaigned on a promise to help the weak and vulnerable.
She also seeks to address Japan's declining birth rates and supports same-sex marriage.
She gave birth at the age of 50 after a fertility treatment and has since pushed to make such treatment more accessible in Japan.
PRODUCED BY: TAN JIA NING