Visa issues

Hey all, think I may have a unique situation and hoping for some advice.

Was married to my Japanese husband while on an Australian Passport but I am a Kiwi living in nz, son born a couple of months after the wedding. To register our son we had to first register our marriage and had a time limit so used my australian passport with maiden name and registered everything in Japan. (Please ignore our stupidity at the time. we were young and had no idea how all this worked).

Anyway my first spouse visa was as my maiden name/australian.

But I am now a full kiwi citizen and using a nz passport with my married name. I want to apply for a new spouse visa but i have no id (and cant get any id) showing my old country/maiden name. My Australian passport would have my married name if i were to go back there and get one.

Kosekitohon has me as Australian/maiden name. Our local town hall told us we cant change the name on the koseki unless we are there and do a name change thing in family court. Also to add NZ its the same apparently.

Any ideas how I can apply for a CoE with my id and kosekitohon having different information? Have contacted my embassy but waiting on a reply still.

Pretty keen to get back to Japan and the paperwork as always is daunting.

Wouldn't you just get your full birth certificate from Australia? (Assuming you were Australian.) I would have thought that would be one of the useful items of documentation required.
Also, your married name is accepted as a convention in places like Aus/NZ and others, you retain your maiden name unless you legally change it.

I was told to apply from another country I need not just my birth cert. But also secondary identification such as drivers license or nz passport which are all in my married name