I’ve been in the process of locating my family koseki. It has been an interesting process. My grandather left Japan for Hawaii when he was 17 years old. He kept Japanese citizenship and had to register every year as an alien in the US. I made several calls to the Japan Consulate. They directed me to the Kumamoto City Hall. I then was directed to the Mashiki Town Hall and finally to Misato Town Hall. I had an old name for Misato. It was Toshine-mura. Thankfully all of the places I called had English speaking staff. Once I gave them my grandfather and great grandfathers birth and death dates, they were able to locate my koseki. It was a miracle!!