@Lilliwyt
From the little I've understood, you can register as a legal partner in some places but not change the family-register, so you'll never be a "family".
@Stormtomte It gives you certain rights as the persons partner but at the same time if I remember right businesses aren't actually required to honor it.
The registry is one the things I've seen argued as being a big issue as far as being able to legalise gay marriage. From what I remember being said is that it is set up in such a way that it is specifically set for man and women marriages and can't be easily changed to factor in same sex unions.
@Heimdal And the same-sex marriage is yet to be generally appreciated by the Japanese society or culture. I think the social acceptance is even bigger and more difficult issue than the legalization.