Political parties and the media widely see the July 12 Tokyo Metropolitan Assembly election as the last and biggest litmus test before a Lower House election that may see the Democratic Party of Japan unseat the ruling bloc.

But the assembly election won't just be a matter of siding with either the DPJ-led opposition camp or the Liberal Democratic Party-New Komeito ruling bloc, because the stakes are different than at the national level, former Tokyo Vice Gov. Yasushi Aoyama said.

"I think it is quite improper to label the assembly election as a prelude battle to the general election. It's just a matter involving the parties," argued Aoyama, a seasoned former metropolitan bureaucrat and now a Meiji University professor.