Looking for grandmother's koseki

Hi, I'm planning a trip to Japan for next year and I am hoping to either find family or at the very least find the birthplace of my Grandmother. She passed away when my father was very young and we do not have very much information about her. Her name is Teruyo Tsubota and all that we know is that she met my grandfather when he was in the army and my oldest aunt was born in Osaka. I'm not sure if that is where my grandmother is actually from or if that is where my grandfather happened to be based. I also was able to find the port and ship that was on when she traveled to America. I have heard about using someone's 'koseki' to find out information but since we do not have a koseki for my grandmother, is there any way to look one up from here in the US?

ANY information or tips woukd be very helpful and much appreciated.

Best,
Christie

There should be a way to apply for Koseki from overseas, but this process requires at least the address where she lived and the proof that you are a relative of her (, and maybe more). If your grandfather is around, it's better to collect more information from him.
Anyway, knowing only her name is a bit too little I think.

If I were you, I'd try to collect as much information as possible, and when arriving to Japan, I'd start by presenting them to a city hall in Osaka Prefecture on a weekday. It would be best if you could write to them in advance.

First of all, if you can get any info, especially addresses, from your grandfather or your aunt or any relative you know, do that.

Secondly, you can try further researching databases such as Ancestry.com or FamilySearch.org. Passenger lists, which were used at immigration, often include addresses of the passengers' contacts in Japan. The typed data is often misspelled, so try to look for the photos of copies of the original handwritten documents.

Now, a koseki is a Japanese national's official record in Japan. Even if the person is deceased, or married or moved out, it will be recorded as the final record on his/her koseki. The thing is that koseki can only be referred to at the city or town of the address, and not the prefecture which is more similar to a state in the U.S. As mentioned, koseki is basically off-limits to non-relatives.

If your aunt was a Japanese national, there is a possibility that some kind of a record of hers exists in Osaka where she was born. You can say the same thing about your grandmother. But again, a koseki has nothing to do with the place the person live(ed).

I wish you luck. Meanwhile, there are migration museums near major ports that you may enjoy visiting. Here is one for Kobe.
https://www.kobe-center.jp/museum.html