That day has yet to come, and legally they are just friends, even though they have lived as a couple for more than five years.

“Right now we are both in good health and able to work, but what if either of us has an accident or becomes ill? We are not allowed to be each other’s guarantors for medical treatment, or to be each other’s heir,” Mr. Kozumi, a 45-year-old office worker, said in a recent interview with his partner, Mr. Aiba, 40. “Progress in Japan has been too slow.”

Ten Japanese municipalities have enacted “partnership” ordinances for same-sex couples to make it easier for them to rent apartments together, among other things, but they are not legally binding. Japanese laws are currently interpreted as allowing marriage only between a man and a woman.

In a society where pressure to conform is strong, many gay people hide their sexuality, fearing prejudice at home, school or work. The L.G.B.T. equal rights movement has lagged in Japan because people who are quietly not conforming to conventional notions of sexuality have been so marginalized that the issue has not been considered a human rights problem, experts say.

“Many people don’t even think of a possibility that their neighbors, colleagues or classmates may be sexual minorities,” said Mizuho Fukushima, a lawyer-turned-lawmaker and an expert on gender and human rights issues. “And the pressure to follow a conservative family model, in which heterosexual couples are supposed to marry and have children, is still strong.”