Opposition parties saw mixed results in Sunday’s Upper House election, with the Constitutional Democratic Party of Japan (CDP) making big gains while others struggled to attract support in a crowded field.

The CDP, which ran on promises to postpone a planned consumption tax hike and raise the minimum wage to ¥1,300, won 17 of the 124 contested seats, gaining eight seats compared with its pre-election level to solidify its status as the leading opposition force in the Diet.

“In less than two years since setting out, we’ve been able to gain so much support,” said party leader Yukio Edano.

Nippon Ishin no Kai, the Osaka-based group pushing to reorganize the country’s 47 prefectures into greater administrative regions, won 10 of the contested seats, expanding its presence in the House of Councilors to 16 seats.

In a sign of the party’s growing appeal, former Tokyo Metropolitan Assembly member Shun Otokita won a seat in the Tokyo electoral district — the first to be secured by a Nippon Ishin candidate outside of the Kansai region.

Osaka Mayor Ichiro Matsui, the party’s leader, said he will continue to push his agenda of “creating a sustainable Japan with a focus on regions” outside of Tokyo.

Meanwhile, the Democratic Party for the People only managed to hold on to six of the eight seats it held going into the Upper House election, as its “Household First” economic platform failed to gain traction among voters.

The Japanese Communist Party came away with seven contested seats compared with the eight it had held previously, while grassroots newcomer Reiwa Shinsengumi, formed in April by actor-turned-lawmaker Taro Yamamoto, saw two candidates with severe disabilities win both of their seats.

“We’ve never seen momentum like this before. The people wanted someone to breathe new life into politics,” Yamamoto said, although he failed to secure his own seat in the election.

Faring worse, the Social Democratic Party won just a single seat — in the proportional representation section — as the party, once Japan’s main opposition party, faces an existential crisis. But it managed to gain 2 percent of the overall votes, keeping its status as a parliamentary party.

The anti-establishment Reiwa Shinsengumi and NHK Kara Kokumin wo Mamoru To (Party to Protect the People from NHK), which gained one seat, saw recognition as parliamentary parties for the first time as they each garnered more than 2 percent of overall votes.

The primary goal of NHK Kara Kokumin wo Mamoru To is to abolish the public broadcaster’s collection of subscription fees and switch to a pay-per-view system for its programs.