Japan is witnessing a growing trend where more women are marrying younger men. The traditional societal norms are shifting, and the increase in these so-called "elder-sister marriages" are becoming more accepted and frequent. While the exact reasons for this change are multi-faceted, factors such as evolving gender roles, changing perspectives about age and relationships, women's late marriage, and their increased socio-economic independence contribute to this nascent social trend.

Traditionally in Japan, marriages where the man is older have been the norm due to gender stereotypes and societal expectations. However, today's Japanese society is progressively changing, with many women choosing to marry later and prioritizing their careers. This trend also challenges the long-standing custom of "yome-san," where wives are expected to be subservient to their elder husband's family.

In contrast, in the US and EU, age disparity in marriages has been less of a societal issue. Marriages where women are older have been common, and the societal acceptance of such marriages is far more widespread. This reflects the more liberal attitudes towards age and gender roles in these countries.