However, it is unclear which party will become the DPJ's ideal partner and whether that party will accept the ruling party's invitation to participate in its coalition government.

Any DPJ failure to reorganize the coalition into a majority government will mean that it is likely to be pinned down by opposition forces on major issues and will face bigger difficulties in pushing forward some of its policies.

Domestic matters have long caused the most heated debates in Japan's upper and lower house elections although diplomatic issues have also quite often been a major topic.

In the latest upper house election, the consumption tax issue dominated the agenda.

The LDP-led former Japanese government once tasted defeat due to its incorrect stance on the consumption tax issue.

Naoto Kan's decision to raise the consumption tax from 5 percent to 10 percent on June 17 was a risky political move that failed to elicit for the DPJ positive opinion from the public.

The results of the latest election show the lack of support from the Japanese public for the current government's efforts to improve its worsening budgetary conditions through raising the consumption tax.

In addition to this long-standing thorny issue, the DPJ-led coalition government's failure to find good solutions to the problems caused by the country's economic slump, slack domestic demand, an ageing society and other issues, also became sources of public grievance.

Given former Prime Minister Hatoyama's setback in his pursuit of a tougher stance with the US, both the DPJ and LDP tried to avoid discussing Japan's relations with Washington in the latest election.

In fact, an agreement has been reached between the two parties to keep unchanged the plan signed between the previous LDP-led Japanese government and the White House on the relocation of the US military base from Okinawa.

Given that quite a few Japanese politicians hope to maintain friendly relations with China, whose status has been on the rise in Japan's diplomatic chessboard, ties with the Asian neighbor also did not become an issue during the latest elections.

The author is director of the Center of Chinese Diplomacy Studies, China Foreign Affairs University.