I thought you said it was a "fantasy" piece? And how did you figure out the year? I know it can't be 19 since there is only 1 known so that leaves 17 and 18.
It is definitely year 18 (1929) according to the Chinese characters. One reads the characters right to left.
When I first saw the coin I thought it looked fake. But, I don't know these coins. Are you sure it is only 4g? Can you confirm this weight?