I like the currency (though Hanako needs money printed of her face sometime), but how does one make a silver coin which is roughly the value of a penny? Even when made of copper-coated zinc, it takes the US Government two cents to make every cent and some other governments are dropping their lowest value denominations. The Japanese have long made the yen (comparable value coin) out of an aluminum blank with a hole in it.
At least in American currency, 90% silver coinage stopped after 1964 except for offerings mainly for coin collectors. Half dollars had 40% silver after that, but only up through about 1970. The Bicentennial Quarter in 1976 had a variant that was 40% silver, but I don't know how common it was. Dollar-level denominations varied between 0%, 40%, and mostly silver, though the latter-most is for collectors.
I don't think that high-content silver coinage for public distribution with values below a dollar/1 KS has been practical for a long time outside of commemorative or collectible coinage.
If you want silver coinage though, Japan does have 100 and even 500 yen coins...so you could have 1KS and 5KS silver coins to emulate that.
This ALL assumes that silver is still a somewhat valuable commodity in the Empire though, and I admittedly don't know much about other nations' coinage.