Diameter 22.7 mm; thickness 3.7 mm; weight 10.28g
N.Jacobs, C.C.Vermeule. Japanese Coinage, N.Y., 1972, Numismatic Review:
The Kaiki Shoho was undoubtedly the first of its kind in the islands and is the oldest surviving Japanese gold coin, there being only one remaining specimen in the collection of the Imperial Household. It was unearthed in the sixth year of Kansei (1794 A.D.) by workmen making repairs on a gateway in the precincts of the Saidaiji Temple of Nara, which was built in the reign of the Empress Shotoku (765 A.D.). This gold coin was kept in the temple as a treasure until the Ninth Year of Meiji (1876) when it was offered to the Emperor Meiji on the occasion of his visit to the temple. Since this time it has remained in the possession of the Imperial family. A small number of exact copies in gold of this coin were made some years ago and are now greatly sought after by collectors.
Kibi no Mabi (693-775 A.D.)
Scholar, author of Chinese prose and poetry, and traditional inventor of Katakana (the first Japanese system of syllabic writing), he went to the court of the Tang Dynasty in China to study in 716 A.D. After this difficult and eventful trip he came back to Japan and took an active part in the government at home and again, as an ambassadors aid, in China (754 A.D.).
Diameter: 23 mm
Most likely it is latest copy.