Japan 1 mon, ND (1668) Kwan-Ei Tsu-Ho "寛" on top on obverse, no symbol on reverse Source: https://pt.ucoin.net/coin/japan-1-mon-1668/?tid=98085
That's pretty cool! I see the 4 mon Kan'ei Tsuuhou with the waves on the back a lot, but I don't run into the uniface 1 mon very often.
I've gotten to the point with cash coins that if it doesn't look like something I've seen before I buy it because it might be interesting. I know very little but it's fun learning more. Anytime there's a type of coin that's hard for people to ID there's strong potential for hidden value.