Looking for Kaz Furumoto last known in Akiku, Hiroshima

Kaz is friend of Roland Kukulka (nickname Frank)(age 88) and Ayako Kukulka (age87) that lived in Westhaven, Michigan USA. Roland and Ayako are both deceased. Last known communication was a letter written by Kaz on September 4, 1989. I am the executor of the Kukulka estate and looking for Ayako's sister, listed as Keiko Yoshizawa from Toyko who is named in the last will and testament. I do not know Ayako's maiden name. I would greatly appreciate any help making contact with Kaz or Keiko, or their family or friends. Please contact me by using the forum Conversation/private message service here if you have any info to help me.

Were there no letters or documents among Ayako's effects which may provide an address?

We do have an address from 1989 and have a letter in the mail. Also thought I would try this forum.