There are two things that make nihonshu unique among the world's alcoholic beverages. One is the process known as heiko fukuhakko, or multiple parallel fermentation. In short, this means that saccharification and fermentation take place simultaneously in the same vat, as opposed to sequentially, as in other fermented beverages. The other thing making sake unique is the use of koji.
Well, sort of. In fact, other beverages in Asia, most noticeably shokoshu and baichu from China, use a form of this marvelous mold. But the way it is done is a bit different.
As readers may recall, koji is a mold that creates enzymes as it grows. These enzymes break starch molecules down into sugar molecules that can be fermented by yeast cells. Koji also breaks proteins down into flavor-enhancing amino acids.