Official campaigning for an upper house by-election in the southwestern prefecture of Oita began Thursday, one of several electoral tests facing Prime Minister Fumio Kishida later this month as he tries to address the unpopularity of his government.

The start of the Oita race will be followed by the kickoff of campaigning for four lower house by-elections next Tuesday. The five by-elections will be held on April 23, along with the second round of local polls to select mayors and assembly members across Japan.

Media polls show that the support rate for the Cabinet has picked up recently, especially since Kishida made a surprise visit to Ukraine, under invasion by Russia for a year, on March 21 for talks with President Volodymyr Zelenskyy.

Supporters cheer for a candidate in the city of Oita as official campaigning for an upper house by-election begins on April 6, 2023. (Kyodo)

The first round of the regional polls will be conducted on Sunday, including gubernatorial and mayoral races in nine prefectures and in six major cities, respectively, and assembly elections in 41 prefectures and 17 big cities.

The focus of the by-elections is on whether voters will support the government's measures to curb the negative impact of recent price hikes and its plans to boost spending for defense and child-rearing policies, which have sparked fears about possible tax increases.

The outcome of the elections is likely to affect Kishida's decision on when to dissolve the lower house for a snap election, pundits said. His Liberal Democratic Party is eager to secure at least three of the five seats -- the number previously held by the ruling party.

The upper house seat in Oita became empty after independent Kiyoshi Adachi, who won the seat with the support of the Constitutional Democratic Party of Japan and other opposition forces, chose to run for the governorship in the prefecture.

Tadatomo Yoshida makes a speech on April 6, 2023, the first day of official campaigning for an upper house by-election in the southwestern prefecture of Oita. (Kyodo) 

Tadatomo Yoshida, 67, a former upper house lawmaker of the main opposition Constitutional Democratic Party of Japan, and Aki Shirasaka, a 56-year-old entrepreneur endorsed by the LDP, have filed candidacies in the race.

At a rally in the city of Oita, Yuko Obuchi, who heads the LDP's Party Organization and Campaign Headquarters, called for party workers to drum up votes for Shirasaka, saying, "We will definitely win." Obuchi is a daughter of former Prime Minister Keizo Obuchi.

Meanwhile, Kenta Izumi, chief of the Constitutional Democratic Party of Japan, criticized Kishida's government for its security policies and response to rising prices.

With Yoshida also supported by other opposition parties such as the Japanese Communist Party and Democratic Party for the People, Izumi said, "We will achieve victory by pushing Mr. Yoshida as the unified candidate" of the opposition camp.

Aki Shirasaka makes a speech on April 6, 2023, the first day of official campaigning for an upper house by-election in the southwestern prefecture of Oita. (Kyodo) 

The four lower house seats up for grabs are the Chiba No. 5 district, Wakayama No. 1 district, and the Yamaguchi Nos. 2 and 4 districts.

The Yamaguchi No. 4 district was held by former Prime Minister Shinzo Abe, who was fatally shot in July 2022. The LDP is backing Shinji Yoshida, a 38-year-old former local city assemblyman, while the Constitutional Democratic Party of Japan has fielded Yoshifu Arita, a 71-year-old former upper house member.

The Yamaguchi No. 2 district was vacated after former Defense Minister Nobuo Kishi, Abe's younger brother, retired for health reasons in early February. His eldest son, Nobuchiyo Kishi, 31, is running in his place.

Hideo Hiraoka, 69, who served as justice minister in a previous government under the now-defunct Democratic Party of Japan, has also decided to throw his hat in the ring. The DPJ is the predecessor of the Constitutional Democratic Party of Japan.

The Chiba No. 5 district election has been called after the incumbent, former LDP lawmaker Kentaro Sonoura, resigned in December over allegations of underreporting political funds. He has also left the ruling party.

The LDP, which is facing an uphill battle in the constituency against the backdrop of Sonoura's political funds scandal, is fielding Arfiya Eri, a 34-year-old former United Nations official of Uyghur descent.

Major opposition parties are fielding their own candidates, having failed to settle on a unified choice.

The Wakayama No. 1 district is up for grabs after Shuhei Kishimoto, a lawmaker of the opposition Democratic Party for the People, resigned to become the prefecture's governor.

Former upper house member Hirofumi Kado, 57, is running on the LDP ticket. Yumi Hayashi, 41, who served as a local assembly member, has been endorsed by the Japan Innovation Party, which has a strong foothold in the Kansai region, including Wakayama.