Looking for mothers family

My mother, Hisae Yokomachi, passed away 5/19. Her wish was that her and my grandmother's ashes are taken back to Japan. Grandma was Taki Yokomachi, I dont know my grand father's name only that he died in WWII.
Couple things I do know... Mom was born in Formosa Jan 1932. I think my grandmother was born in Nagasaki. And in 1957 they lived in Tokyo, where I was born.

You don't have any old letters, documents, passports, photos, etc that might provide some other clues?

I have to tell you, even if you successfully locate them there is a possibility they will not be interested in hearing from you or open to the idea of placing their ashes in the family tomb. Then again, they may be thrilled.

You don't mention brothers or sisters, so there is a possibility there are no cousins or other similarly close relatives remaining alive today anyway.

Even if you don't succeed in finding relatives, it is still possible for you to repatriate their remains and have them placed in a cemetery here. It essentially comes down to money and maybe a little paperwork.