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Paper short abstract

This paper analyzes Japan’s marriage equality cases as constitutional transformation shaped by European marriage alternatives and U.S. developments following Hawaiʻi’s Baehr v. Lewin, highlighting the limits of incremental reform in Japan.

Paper long abstract

This paper examines Japan’s marriage equality litigation as a site of constitutional transformation shaped by transnational legal dialogue, particularly Japanese courts’ engagement with European marriage and partnership regimes and subsequent legal developments in the United States following early litigation in Hawaiʻi. Between 2021 and 2024, Japanese district and high courts issued a series of decisions assessing the constitutionality of excluding same-sex couples from marriage under the Civil Code and the Japanese Constitution. While outcomes diverged, these decisions reveal a shared judicial effort to reconcile constitutional text with evolving social norms by drawing on comparative law and foreign experience.

Japanese courts have repeatedly referenced European jurisdictions as early innovators in recognizing same-sex relationships through civil unions, registered partnerships, and marriage equality. These European models have been cited to demonstrate shifting global understandings of family, equality, and state recognition, while also informing debates over whether incremental alternatives to marriage can satisfy constitutional equality guarantees. At the same time, courts have acknowledged legal developments in the United States that followed the Hawaiʻi Supreme Court’s landmark decision in Baehr v. Lewin (1993), which catalyzed global constitutional conversations on marriage equality and influenced subsequent judicial and legislative reforms. Together, Europe’s experimentation with marriage alternatives and Hawaiʻi’s role as a constitutional catalyst form an important comparative backdrop for Japan’s contemporary litigation.

The paper argues that Japan’s reliance on local partnership and “familyship” systems—adopted in the absence of national legislative reform—mirrors earlier European approaches while raising unresolved constitutional questions about whether alternatives can substitute for marriage without entrenching inequality. By situating Japanese case law within this transnational context, the analysis highlights how courts selectively deploy comparative references to legitimize constitutional interpretation while maintaining deference to legislative discretion.

Through doctrinal analysis and socio-legal comparison, this paper positions Japan as a late but revealing participant in a global constitutional conversation on marriage equality. It demonstrates how European precedents and U.S. legal developments inform Japanese judicial reasoning, while Japan’s ongoing litigation offers insight into the limits of incremental reform and the future trajectory of constitutional change in aging, industrialized democracies.