The following explains how members of the Diet's House of Councillors are elected in the Sunday election.
Lawmakers in the House of Councillors, the upper chamber of Japan's bicameral legislature, serve six-year terms. An election in which half of the chamber's seats are contested takes place every three years.
A total of 124 of 248 seats will be up for grabs this round, together with one to fill a vacancy in the other half. The chamber had 245 seats, but three were newly added as part of electoral system reform.
Members of the upper house serve a full term, unlike lawmakers in the House of Representatives, or lower house, which a prime minister can dissolve for an election at their discretion.
Its shorter, four-year term means the lower house is thought to more directly reflect the will of the people than the upper house. Japan's Constitution thereby grants more power to the lower house by giving its decisions precedence over those of the upper house.
Voters cast two ballots in the election -- one to choose electoral district representatives for 74 of the upper house's 124 contested seats and one under a proportional representation system to fill the remaining 50 seats with parties' list candidates.
Under the proportional representation system, voters write in either the name of a political party or a specific candidate from contenders registered by parties in an open-list system.
List seats are allocated to parties in proportion to the number of ballots they receive, either in the party's name or candidates on their list.
Once the number of seats to be allocated to each party is clear, candidates are ranked within each party according to the number of ballots they received by name. Those with the most votes will be given top priority in filling the list seats allocated to the party.
A "special quota" was introduced from the last upper house election in 2019 for the proportional representation system, through which candidates can also be elected according to their place on a list submitted by each party, regardless of the number of votes they get.
Candidates cannot run in an electoral district and under the proportional representation system simultaneously, unlike those running in lower house elections.
The minimum voting age was lowered to 18 from 20 in an amendment that took effect in 2016.