Campaigning began Tuesday for the Oct. 22 House of Representatives election, pitting the ruling coalition led by Prime Minister Shinzo Abe against a recently reorganized opposition lineup including Tokyo Gov. Yuriko Koike's Party of Hope.

Reforms have shrunk the lower house by 10 seats to a postwar low of 465. Abe has said he will resign if his Liberal Democratic Party and its smaller coalition partner Komeito do not win an overall majority with a combined 233 seats.

When he dissolved the lower house on Sept. 28, Abe said he needed to get a fresh mandate for his administration's handling of heightened tensions over North Korea, as well as its decision to spend more of the revenue envisioned from a planned consumption tax hike on social welfare and less on paying down government debt.

He called the election before the lower house members' current term ends in December 2018 apparently aiming to give the opposition as little time as possible to mount a united challenge to the ruling coalition he has led for nearly five years, though it has triggered a realignment of opposition forces.

Since then, the Party of Hope has vowed to take down the Abe administration, distinguishing its own "reform-minded conservative" platform from that of the coalition by promising to freeze the tax hike scheduled for October 2019, tax retained corporate earnings and eliminate Japan's nuclear power plants by 2030.

Koike, who was a lawmaker with the LDP before she ran for governor last year, has said she will not quit her current job to return to the lower house.

With the Party of Hope still having not specified its pick for preferred prime minister in lieu of Koike, voters choosing the party may have to accept a degree of uncertainty and bet on her being able to smoothly lead the party from outside the Diet.

The main opposition Democratic Party has split, with more than 100 of its conservative-leaning members being allowed to join the Party of Hope and its more liberal members forming the new Constitutional Democratic Party of Japan, led by former chief Cabinet secretary Yukio Edano.

Both the LDP and Party of Hope are in favor of amending the war-renouncing Japanese Constitution for the first time since it came into force in 1947, but the LDP has put a greater emphasis on adding an explicit mention of the Self-Defense Forces in the document after having pushed security legislation through the Diet last year to expand the troops' roles.

The CDPJ argues that the security legislation introduced by the Abe administration is unconstitutional, and for that reason opposes adding a mention of the SDF's status in the Constitution. It has said it will not field candidates in districts where those hailing from the Democratic Party are running.

Democratic Party leader Seiji Maehara and other senior members are set to run as independents.

Other parties include the Japanese Communist Party, the Social Democratic Party, the Japan Innovation Party and the conservative Party for Japanese Kokoro.

Voters get two ballots and must write in the name of a party on their proportional representation ballot and the name of a candidate on their electoral district ballot.

Candidates running in single-seat constituencies, which account for 289 of the 465 seats, are allowed to run on proportional representation lists at the same time, giving them a chance to win a seat even if they lose in their districts.

The 176 seats allotted through proportional representation are split into regional blocks.

Laws passed in the House of Representatives are referred to the smaller House of Councillors, or upper house, which cannot be dissolved at will by the prime minister. Half of its 242 seats go up for re-election every three years.


How are members of Japan's House of Representatives elected?

Under the revised electoral law that took effect in July, the number of lower house seats has been reduced to 465 from 475.

The revised Public Offices Election Law, aimed at reducing voting weight disparities between densely and sparsely populated constituencies, redrew district boundaries in 97 electoral districts in 19 prefectures nationwide.

Out of the 465 seats, 289 are elected from single-seat districts and the remaining 176 through proportional representation in 11 regional blocks.

Each voter casts two ballots at a polling station -- one to choose a candidate in a single-seat constituency and the other to select a party for proportional representation.

A candidate who runs in a single-seat district can also appear in the candidate list of the proportional representation system.

Even if such a candidate loses in the constituency, he or she could still secure a seat under the proportional representation method, if the candidate's party gains sufficient votes, in a system dubbed a consolation round.

Political parties and groups, which have five or more Diet members or gained 2 percent or more of the total valid votes in the previous national election, can submit lists of candidates for the proportional representation section beforehand and will be given seats in accordance with their share of regional block votes.

They will then grant the block seats to candidates based on the order in which the lists are drawn up.