It really would need someone with access to military records, deployment lists, social security records, or other kinds of private information. If the name were a super rare name, you might get lucky by trying to find someone with the same name on Facebook or Twitter or Instagram, but Kameda isn't such a rare name. As mdchachi says above, if you are interested in repatriating the flag back to the descendants or relatives of the original owner, you can try the Obon Society, which has some resources to track down relatives. Or, you can also try the Japanese Embassy, which now has a website where you can contact for enquiries like this.