In the decades since the Eldritch War, the Seasons Calendar has become the communal way to mark the days, no matter the race or origin of those that call the world of Isekai their home.
Centuries before even the Divine Races of Isekai would set foot upon the land, the gods found themselves divided by their tenets, choosing to fall in line with those others that shared their thoughts.
The large Kingdoms of Isekai agreed upon a standard trade for the value of metals. This allowed each area to mint their own coins with images and historical icons but still have them be useful during trade during travels to far off lands.
We trade anything, from weapons and gems to simple paper and crops. Someone, somewhere will pay a pretty coin for our goods.— Unknown
Trade agreements across Isekai govern the paths of trade that cross borders and span continents, but no agreement could set the precedent that came from the first trade agreement between the surface and Káto.