Tears welled up in Kaori Oguni¡¯s eyes as she recalled the heartache she felt at what was supposed to be one of the happiest moments of her life ¡ª that is, when she and her husband registered their marriage at a Tokyo ward office in 2006.

¡°As I was completing my paperwork, all I could think of was, ¡®OK, that¡¯s it then. This is officially goodbye to my family name,¡¯ ¡± Oguni, a 41-year-old mother of one, said in a recent interview. ¡°A family name is an important part of my identity. Losing it was painful.¡±

Oguni is one of five people suing the government over what they call a ¡°sexist¡± civil code that has traditionally resulted in Japanese women changing their surnames upon marriage. It requires Japanese couples to register their marriage under a single surname.