Nippon Ishin no Kai adopted an action plan on Saturday seeking to push Prime Minister Shigeru Ishiba's ruling coalition into a minority in the House of Councillors in an election in the summer.
"I will accept any outcome and take responsibility in the end," Nippon Ishin leader Hirofumi Yoshimura said at a party convention in Tokyo, referring to the Upper House election.
The ruling coalition already lost its majority in the House of Representatives, or the Lower House, in last year's election.
Yoshimura said that Nippon Ishin will work hard to follow through on its campaign pledges, including social security reform. He also said the party will promote discussions on amending the country's Constitution, including its war-renouncing Article 9.
Nippon Ishin co-leader Seiji Maehara said that the party has decided to vote in favor of the government's fiscal 2025 budget, based on an agreement with the ruling coalition to modify it.
"We are not a complementary force to the ruling coalition. We made a political decision to realize our way of thinking," Maehara said.
The action plan says that the ruling coalition's defeat in the Lower House election paved the way for Nippon Ishin to realize its policies including free education.
Nippon Ishin will pursue achieving further campaign pledges by pushing the ruling coalition into a minority force in the Upper House, the action plan says.
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