As Prince Hisahito of Japan crosses the threshold of adulthood at twenty, his government has chosen the moment not merely to celebrate an heir, but to reaffirm an ancient ordering of power — one that reserves the Chrysanthemum Throne exclusively for men. The timing is no accident: Hisahito, the first male born to the imperial family in four decades, has long been the living answer to a question Japan nearly resolved differently. In reinforcing male-only succession at this juncture, the government signals that continuity, not reform, will define the institution's future — at least for now.