1st thing is how do you plan to get married?
Register at local Japanese cityhall under Japan law or at US base/US,under US law?
Different sets of documentation/requirement.
As for changing status to Sofa, you better ask your US Fiance about the proper procedure/documentation.
Googling your question :-https://www.jag.navy.mil/legal_services/documents/SOFA%201%20-%20Updat...
If you are under Japanese immigration status other than Permanent Resident, you may
switch your status to SOFA by following the steps below:
1. Complete the attached USFJ Form 8EJ, Confirmation of Eligibility under SOFA, and have your
sponsorfs command complete the backside of the form under gFor the United States.h
2. Visit the local Japanese Immigration Office with the following items:
- Valid passport
- Dependent ID card
- Residence card (if applicable)
- Certificate of permission to engage in more activities than allowed by their visa (if applicable)
- Letter of dependency (for military memberfs dependents)
- Letter of employment with dependent information (for civilian employeefs dependents)
- Completed USFJ Form 8EJ
3. Receive the USFJ Form 8EJ completed by the Japanese Immigration Office. If you turns in
your resident card, ask the immigration officer for the card back after they invalidate it.
4. Visit the PSD Passport Office with the USFJ Form 8EJ, passport, letter of dependency (or letter
of employment for civilian employees), and invalidated Japanese resident card (if applicable), and
obtain a "multiple exit/reentry" stamp on your passport. PSD Yokosuka is on the 3rd Floor of
Bldg 1555. PSD Sasebo is in Bldg 200 and can be reached at DSN 252-2200.