I got interested and am now overthinking this, probably. Got some questions? Never even HEARD of this before today.
I understand the cooking/cooling process for these charcoals.
Looking at the 30 varieties offered at Korin, I see the hierarchy being, first, whole branches yielding about .75" or 20mm sticks of round charcoal, then halved larger branches split to smaller size, then split logs, finally, lump charcoal of irregular size/shape and lastly, for the undiscerning gaijin such as myself, extruded sticks of ground charcoal (Kingsford 様式).
Round sticks = most burning surface per approximate same dimension/weight of sticks, which might = highest heat output, other factors being equal?
If any have knowledge of the sourcing of wood for this product? Are trees grown and harvested solely for this use, perhaps as the smaller branches harvested from "copiced" oak trees as was done in pre industrial age Europe?
https://en.m.wikipedia.org/wiki/Coppicing
Or is wood for this charcoal a byproduct of trees felled whole for other uses, made from the slash and trim of trunks destined for use as lumber?
If the wood is being harvested primarily for charcoal making, do the foresters prefer to do this at a particular TIME OF YEAR? Summer harvested wood has significant ammounts of sugars and other chemicals stored in the sap wood, plus the bark falls off easily upon drying. Winter harvested wood will have less sugar & etc. in sapwood and the bark will remain tight to the pieces.