TOKYO, July 3, 2025 (BSS/AFP) - Campaigning for Japan's upper house election started Thursday, with unpopular Prime Minister Shigeru Ishiba fighting to maintain the ruling coalition's majority.

Ishiba, 68, has been head of a minority government since October when he led the long-dominant Liberal Democratic Party (LDP) to its worst general election result in years.

The ruling coalition of the LDP and the smaller Komeito party could lose its majority in the upper house too on July 20 when 125 of the 248 seats are up for grabs.

If this happens, "Ishiba may need to step down, leading to a new LDP party leadership election and a new premiership election," Toru Yoshida, politics professor at Doshisha University, told AFP.

However, "the opposition bloc...don't appear to be willing to align to take office", he said, adding that "a grand coalition" between the LDP-Komeito bloc and the CDP could emerge instead.

Voters are angry about inflation -- rice prices have doubled in the past year -- and corruption within the LDP. US tariffs are also causing unease among firms.

Yoshihiko Noda, leader of the largest opposition Constitutional Democratic Party of Japan (CDP), promised voters: "We'll save you from inflation."

"Let's change Japan, let's overthrow the Ishiba administration," Noda said in the southern prefecture of Miyazaki.

The LDP's ruling coalition, which currently holds 141 upper house seats, needs to win at least 50 of the seats on offer to maintain its majority.

Smaller opposition parties could do well, including the Democratic Party for the People (DPP), which wants to cut sales taxes, and the anti-immigration Sanseito with its "Japanese First" slogan.

Both the DPP and Sanseito, as well as the CDP, gained seats in the Tokyo assembly elections last month when the LDP lost its position as the largest party.