Once United States Citizenship and Immigration Services (USCIS) approves a petition, the petition will be forwarded to the National Visa Center (NVC). The NVC will send the visa applicant instructions asking to prepare all of the required forms, documents and payment of fees. Once the NVC has received all of the forms and documents, they will review and schedule a visa interview appointment. The NVC then forwards the case file containing the petition, forms and documents submitted by or on behalf of a visa applicant, to the Immigrant Visa Unit of the U.S. Embassy, Tokyo or the U.S. Consulate General, Naha where the applicant will be interviewed.
For details about immigrant visa processing through the National Visa Center, please see here.