How do I find a relative that is not listed in WWII archives?

You might try the ABMC Burials and Memorializations website at https://www.abmc.gov/database-search .  You can search by first and last name.  Good luck!

Dear Ms. Wills,

Thank you for contacting History Hub with your inquiry. He may have a record in our Individual Deceased Persons Folders series. These are not all listed in our searchable database. You can write in to stl.archives@nara.gov with the details of your cousin (full name, date of birth, date of death, service number, as much identifying information as you know) and we will conduct a search for this record. Here is a link to provide some more information about what is in these records; https://search.archives.gov/search?query=IDPF&submit=&utf8=&affiliate=national-archives