Japan's ruling party scored a sweeping victory in Sunday's House of Councillors election, helping pro-constitutional amendment forces retain the two-thirds majority needed to push for revising the supreme law, an unaccomplished goal of former leader Shinzo Abe whose assassination days earlier shocked the nation.

Prime Minister Fumio Kishida's Liberal Democratic Party grabbed 63 seats, or more than half of the 125 seats up for grabs, buoyed by strong voter support in a show of public confidence in his nine-month-old administration despite the country struggling with rising prices and security threats posed by Russia's war in Ukraine.

In all, the LDP and its coalition partner Komeito secured a total of 76 seats, comfortably retaining a majority in the 248-member upper chamber of parliament.

Prime Minister Fumio Kishida as head of the ruling Liberal Democratic Party shows the names of candidates certain to win seats in the House of Councillors election on July 10, 2022, at the party headquarters in Tokyo. (Kyodo)

The pro-constitutional amendment camp, comprising the LDP-Komeito coalition, two opposition parties and independents, secured 179 seats in the upper chamber. Combined with the 84 seats it holds that were not up for election this year, it crossed the 166-seat threshold needed to aim for a first-ever revision of the 1947 Constitution.

But while the LDP had its best outcome since 2013, the major opposition party, the Constitutional Democratic Party of Japan, won just 17 seats, losing six of the contested seats it had held before the election.

The opposition Japan Innovation Party, which advocates constitutional reform, won 12 seats, adding six to its total in the chamber.

At the LDP headquarters in Tokyo on Sunday, Kishida and senior party executives offered silent prayers for Abe, Japan's longest-serving premier who died Friday after being shot by a man when giving a speech in Nara, western Japan.

"The election, which is the foundation of democracy, was challenged by violence and it carries a big meaning that the election was carried through. I will continue to work hard to protect democracy," Kishida said, in reference to the shooting of Abe.

Kishida also vowed to push ahead with plans for amending the Constitution, saying, "We will deepen parliamentary debate over the Constitution further so a concrete amendment proposal can be compiled."

The LDP's constitutional reform proposals include amending the war-renouncing Article 9, a sensitive issue for South Korea and China, both of which suffered from Japan's wartime militarism.

The ruling party aims to end the debate over the constitutionality of the Self-Defense Forces by explicitly mentioning them in the supreme law.

Kenta Izumi, leader of the main opposition Constitutional Democratic Party of Japan, speaks during a TV interview at the party's election operation center in Tokyo on July 10, 2022. (Kyodo)

CDPJ leader Kenta Izumi acknowledged defeat, saying, "I took it as the voters not wanting to switch from the LDP and entrust us with running the government."

Speaking in a press conference which started in late hours of Sunday, Izumi said party executives bear responsibility for the outcome but that he would not quit as party chief.

Despite the Japan Innovation Party gaining seats, its leader Ichiro Matsui also described the result as a defeat, saying the LDP scored an "overwhelming victory."

Matsui, who had said earlier he would step down after the election, said the LDP "needs to set a schedule (for revising the Constitution), which the late former Prime Minister Abe would have wanted to see."

Kishida took office last October pledging all-out efforts to cope with the COVID-19 pandemic.

The fresh mandate will also enable him to proceed with his drive to create a "new capitalism" designed to redistribute wealth, with no national election expected until 2025 unless Kishida dissolves the House of Representatives, the more powerful lower chamber.

The prime minister is expected to reshuffle his Cabinet and ruling party executives by September, according to LDP sources.

The killing of Abe, a lower house member and a key LDP figure, rocked the nation and the world, unifying major parties in their resolve not to yield to political violence.

The shockwaves are expected to reverberate in Japan's political world, with the LDP losing one of the staunchest supporters of constitutional reform and an advocate of more defense and fiscal spending to raise the country's global standing.

The behavior of swing voters had been another focus of the election. Voter turnout was 52.05 percent, higher than 48.8 percent in the previous upper house election 2019.

According to an analysis of the Kyodo exit polls, the LDP garnered the biggest share of unaffiliated voters in the proportional representation section at 21.9 percent, followed by 17.7 percent for the Japan Innovation Party.

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Voters fill out their ballots for Japan's House of Councillors election at a polling station in Osaka, western Japan, on July 10, 2022. (Kyodo)

The election saw limited cooperation among opposition parties, which had previously joined forces to prevent splitting the vote.

The Democratic Party for the People had been cozying up to Kishida's LDP, despite the small opposition party sharing the support base of the country's biggest labor organization Rengo with the CDPJ.

Elections are held for half of the upper house seats every three years. A total of 545 candidates vied for the 125 seats -- 74 in electoral districts and 50 chosen by proportional representation, plus one vacancy among the seats in the other half of the chamber. The total included a record 181 female candidates.

Ruling and opposition parties had sparred over ways to help households hit by the rising cost of living, partly blamed on Russia's military aggression in Ukraine and a weak yen and seen as a rare occurrence in a nation known for deflationary mindsets among firms and consumers.

Parties differed on how Japan should bolster its defense to cope with increasing security threats highlighted by the Ukraine crisis, an assertive China and a nuclear-armed North Korea.

The LDP pledged to strengthen Japan's defense capabilities with an eye on boosting its defense budget to 2 percent or more of gross domestic product.

That stance contrasted with Komeito and the CDPJ, which see the need first to discuss the substance, not size, of defense spending.

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