Party leaders rallied voter support in various parts of Japan on Saturday, wrapping up more than two weeks of official campaigning for the upper house election.

Prime Minister Shinzo Abe, who heads the ruling Liberal Democratic Party, has pushed constitutional reform as one of the main issues for Sunday's House of Councillors election in which 370 candidates will vie for 124 seats.

But the public pension system also came under intense scrutiny after a government report estimated that under the current arrangement a retired couple would face a 20 million yen ($185,000) shortfall if they live to be 95 years old.

Social security costs are expected to continue to rise in Japan, as the debt-ridden country grapples with the rapid aging of its population.

"The pension system is a big issue. The opposition bloc is only raising concerns but we will secure funding (to make the pension system sustainable) with a sense of responsibility," Abe said in his final stump speech in Tokyo's Akihabara district, a hub of subculture, where he has previously concluded campaigns in recent national elections.

The opposition camp, meanwhile, criticized the Abe government for having refused to accept the report because it contradicts the government's view that the pension system is the basis of household finances during post-retirement years.

In addition to the pension issue, the country's ruling and opposition parties remain divided over key issues such as whether to amend the pacifist Constitution and if the consumption tax should be increased from 8 percent to 10 percent in October as planned.

Natsuo Yamaguchi, who heads the LDP's coalition partner Komeito, pledged to improve social security. "We will use the consumption tax to make preschool education and child-care services free of charge," Yamaguchi said in Kobe, Hyogo Prefecture in western Japan.

While polls indicate a solid win for the ruling coalition, opposition parties have been scrambling to highlight their differences on the key issues during the 17-day campaign.

Hoping to coalesce the anti-LDP vote to become a viable counterbalance to the ruling coalition, opposition parties are joining forces by fielding unified candidates in all 32 single-seat districts across the country.

"One more step will get us closer to bringing (the focus of) politics back to our livelihoods," Yukio Edano, leader of the main opposition Constitutional Democratic Party of Japan, said in a speech in Tokyo.