Last month the Supreme Court handed down its verdict on a lawsuit filed by people who objected to the Civil Code requirement that married couples be registered under one surname. The majority of the 15 judges ruled that the plaintiffs' rights were not being violated by the law, and the media debate that followed pivoted on the question of constitutionality versus culture, or the assumption that Japan had some unusual social need for couples and their children to be identified by one name only.

Within this discussion, Sota Kimura, an associate professor at Tokyo Metropolitan University and presently one of the most in-demand media pundits when it comes to constitutional matters, brought up the wording the judges used in their decision. On various media, Kimura pointed out that this is the first time the Supreme Court has ruled on a case concerning Article 24, which defines marriage as a legally binding union between two people who mutually agree to enter into that union. Although English translations of the Constitution typically describe marriage as involving "both sexes," the word ryōsei can also be interpreted to mean "two parties," and Kimura believes it was this interpretation the judges were stressing. While the court said there is nothing unconstitutional about compelling married couples to register under one name, they didn't expressly limit marriage to a man and a woman.

According to Kimura, if a same-sex couple someday sues the state to have their marriage legally recognized, lawyers can use this ruling as a precedent to claim that such a union is guaranteed by the Constitution. He is certainly aware of Prime Minister Shinzo Abe's remark that the Constitution would have to be revised before same-sex marriages can be permitted in Japan, but the Constitution does not use the word danjo (men and women), so it is not manifestly apparent that the two "parties" have to be of different genders.