The House of Councillors has 242 members, elected to six-year terms. Half of the seats of the House, 121 seats, will be up for election this summer.
Seats are divided between electoral district (senkyoku) seats and party proportional (hireiku) seats. There will be 73 district seats and 48 party proportional seats up for election.
In the House of Councillors elections the electoral districts are contiguous with the boundaries of the prefectures. Each prefecture has a least two House of Councillors members representing it, which means prefectures will thus have at least one seat up for election this summer. The maximum number of seats up for election in an electoral district is 5.
There are 29 prefectures with but a single seat up for election, 12 prefectures with two seats up for election, 5 with three seats up for election and a single prefecture (the Tokyo Metropolitan District) with five seats up for election.
The prefecture with the greatest electoral leverage will be Tottori, where one House of Councillors member will be elected to represent the interests of just 590,000 inhabitants. By contrast, voters in Kanagawa Prefecture (3 seats) must accept having one House of Councillors member for every 2.98 million inhabitants.
Two prefectures, Gunma and Tochigi, will be losing seats in this election through reapportionment, each prefecture dropping from two seats to one. This means that two sitting incumbents could be in the running for but a single seat. In both Gunma and Tochigi, the two existing seats are split between a member of the ruling Democratic Party of Japan and a member of the Liberal Democratic Party. Expect rowdy campaigns in these two prefectures, one of which (Gunma) is considered an LDP fortress, the prefecture having produced a slew of prime ministers for the LDP.
Two prefectures, the TMD and Chiba, will be adding seats in this election. This would normally be a plus for the LDP, which in recent elections has been able to rely on its political machine to scrape into office in multi-seat districts with second place or third place finishes. However in 2007, the LDP, running two candidates in the TMD, only managed to win one seat, this despite the expansion of seats available from four to five. The LDP's top vote getter, TV announcer Marukawa Tamayo, only barely finished above an independent, AIDS activist Kawada Ryuhei, in the battle for fourth and fifth places. Kawada has since joined the Your Party (Minna no To) which advocates policies resonant with the values of urban and suburban managerial-class and salarymen-class voters. With the LDP's political machine in tatters and the Your Party riding high in the polls, the Your Party candidate will overleap the LDP candidate, leaving the LDP likely fighting minor parties and independents for the newly available seat - a battle the moribund LDP could lose.