The number "roku" (six) has been used since ancient times in words like "rokuho" (six directions) and "rokudai" (six great things), which refer to nature and the world, and "rokutoku" (six virtues) and "rokuho" (six laws), which represent natural principles and laws, making it a harmonious number that is neither too much nor too little. "Gen" (玄) refers to a bundle of threads dyed a deep, rich black. By extension, it has come to mean "profound," "deep," and "quiet." A person with advanced skills and knowledge is called a "kurojin" (expert), and "rokugen" refers to a well-balanced sake produced by the skilled techniques of a master brewer.