Japan electoral district and seat reform

Following the 2025 Census, Japan’s Ministry of Internal Affairs and Communications reported significant vote disparities across the House of Representatives. Data indicated that 18 constituencies in 11 prefectures showed disparities exceeding double the benchmark set by the Tottori 1st District. In response, the House of Representatives Electoral District Boundary Commission is expected to review boundaries, potentially redrawing districts in 13 prefectures to mitigate these gaps.

Negotiations regarding the reduction of seats in the House of Representatives have intensified. While the Liberal Democratic Party (LDP) previously proposed reducing proportional representation seats by 31, the Democratic Party for the People has countered with a proposal to reduce only 19 seats. The opposition party argues that seat calculations should be based on confirmed 2025 population data rather than 2030 projections. LDP Diet Affairs Committee Chair Murai has expressed strong interest in passing reform legislation during the current Diet session.

Technical debates have also emerged regarding the proportional representation allocation method. Proposals include switching from the D'Hondt method to a modified Sainte-Laguë method, which could potentially assist smaller parties in gaining seats. Furthermore, there is a proposal to raise the minimum vote threshold for candidates from one-tenth to one-sixth of valid votes. While some parties are open to these technical adjustments, others have voiced opposition to the possibility of leaving seats vacant if a party fails to field sufficient candidates.