пока гуглил, нашел вот что:
Certification as to the marriage
By a delivery of an authorized copy of certification as to the marriage issued by the foreign land (state / nation), the marriage is regarded under law of Japan as one in accordance with the formality of the foreign land.[5] As the additional required documents, Japanese government requires foreigners(non-Japanese citizen) to provide a sworn Affidavit of Competency to Marry, which is issued by their original country's embassy.[9]
т.е. даже со справкой о браке из другой страны может потребоваться та злосчастная справка из России о пригодности к браку, для того, чтобы Япония признала брак, заключенный полностью за рубежом