There is no problem whether you go through the procedures in Japan or Thailand first, but it is better to go through the procedures in Japan first to save time and effort, so here is an explanation of the procedures in Japan first.

1. Register your marriage at the municipal office of your place of residence or domicile.

If you are Japanese, you will need a copy of your family register if you are submitting it to a municipal office other than your domicile, but other than that, you basically do not need it.

Thais will need to prepare the following documents

A. A certified copy of the residence registration (Bai Thabien Baan) or a certificate of the national registration (Bebu Laproon Raingarn Thabien Ratchadorn) (one copy in English and one in Japanese translation is required). This can be obtained at the county office where the Thai national is registered.

B. Certificate of Eligibility for Marriage (one copy in English and one copy in Japanese).
In case of obtaining the certificate at the Thai Embassy in Japan, the following documents are required
Copy of passport with valid visa
Photo
Thai ID card and copy
Copy of residence registration (Bai Thabien Baan)
Certificate of Singleness – English or Japanese translation required and Garuda seal (seal of recognition from the Kingdom of Thailand)
Certificate of Divorce (for those who have been divorced)

C. Certificate of Divorce (English or Japanese translation is required if the applicant has been divorced)

D. If you have changed your name or surname, the certificate (English or Japanese translation is required)

E. If the applicant is under 20 years of age, written consent from the parents.

F. Declaration of Marriage This is a document in which the person swears that he or she is eligible for marriage. The declaration does not need to be certified by the Ministry of Foreign Affairs of Thailand, even if the original is in Thai. (One copy of Japanese translation is required).

The certificate issued by the District Office of Thailand is in Thai language and should be translated into English and Japanese for submission to Japan. The original Thai document and the English translation must be certified by the Ministry of Foreign Affairs of Thailand. The Japanese translation does not need to be certified, only the translation is acceptable.

Please do not submit the original copy of the residence registration certificate, divorce registration certificate, name change certificate, etc. If you submit the original documents, they may not be returned to you and you may have problems in the future. Please make sure you submit a copy of the document with the seal of the county office that issued it.

2. Submit a copy of your family register to the Japanese embassy in Thailand and ask for a marriage certificate.

Required documents:

Family register (issued within 3 months), Thai spouse’s ID card (original and copy), Thai spouse’s residence registration card (original and copy), Thai spouse’s passport (original and copy (not required if spouse has not obtained ID page)), Power of Attorney (if Japanese spouse cannot come to the Japanese Embassy at the time of application). (If the Japanese spouse is unable to go to the Japanese Embassy at the time of application, the letter of attorney must be signed and sealed by both the authorizer and the assignee (the authorizer must write the name of the assignee in the body of the letter of attorney).

3. Register the marriage at the Thai county office.

register the marriage at the County Hall of Thailand. 4. translate the previously issued English marriage certificate into Thai and have both certificates attested by the Ministry of Foreign Affairs of Thailand. The marriage certificate (in English) and the Thai translation are then taken to the county office where the Thai spouse resides to register the marriage.

Please note that if you have already registered your marriage in Japan, you will not be issued with a marriage registration certificate, which is issued if you have already registered your marriage in Thailand.
If you wish to live together as a couple in Japan, you will then need to apply for a visa (status of residence) from the Immigration Bureau.