The difference between sake and Shochu
First of all, sake is fermented, Shochu is distilled. In other words, if we just consider the production process, Honkaku Shochu is to sake what brandy is to wine.
Sake, which in Japanese is called Nihonshu, is the product of rice alcoholic fermentation in water, with the help of selected microorganisms.
Sake has approximately 2000 years of history and was initially developed in the rice producing regions, that enjoy a winter climate compatible with the control of alcoholic fermentation. The history of Honkaku Shochu starts much later. Most likely, when distillation technology reached Japan, sometimes between the 12th and the 14th centuries.
Perhaps, Shochu started as distilled sake or distilled sake-kasu, which is the residual of rice fermented must after pressing, during sake production process.