Japan's largest opposition group unveiled a campaign platform on Wednesday that said it would stand for rights like supporting same-sex marriage and different surnames for couples, marking out differences with the conservative ruling party.

The Constitutional Democratic Party of Japan (CDP), led by Yukio Edano, is facing a critical test in the Oct. 31 general election, the first it is contesting in its current form since its formation last year, hoping to make a dent in the ruling party coalition that holds a clear majority in the Diet.

But it is struggling in opinion polls, and with the ruling Liberal Democratic Party (LDP) also emphasizing social safety nets and similar policies long espoused by the Democratic Party from which the CDP was formed, it is facing a battle to stake out its own territory.