Japanese Fantasy Coin

At the obverse placed legend of Japanese coin issued in 848 AD. But real coin has size 20-21.5 mm (look quotation below).
Shown here item is fantasy coin.

Image received from Jim Farr.

Abridged history of the copper coins of Japan by Leon van de Polder, 1891 (from The East Asia Journal, 7, 1982):

In the 10^th month of 1^st year of Kasho (A.D. 848) His Majesty by decree proclaimed that by order received from Heaven the denomination of the year would be Kasho and that the coins in use hitherto getting very old, the order from above was also to see to it and to make a new cash which named Chonen-taiho. This piece was to be worth 10 of the old cash and it was ordered to use it as well as the former. It was made from off this year till the 2^nd year of Ten-an (A.D. 858).
Two different kinds were made, viz.:
1^st had a diameter of over 6 bu or 18.5 mm and weighed over 5 fun or 29.15 grs.troy.
2^nd had a diameter of over 6.5 bu or 20 mm and weighed 4 fun or 23.32 grs.troy, but it seems that some were minted having a diameter of 7 bu or 21.5 mm and weighing 8 fun or 46.64 grs.troy.