The koji breaks down the polysaccharides in the rice to disarracharies giving it a very sweet taste. Try to avoid drinking too much of the amasake drinks made with almonds or nuts as they can be hard on the digestion. Stevia is just one of the more popular ones. Perhaps Consumer Direct can help in that area. It is a little expensive in large amounts.
Brown sugar is usually white sugar mixed with molasses or sprayed with caramel coloring.
Raw sugar is often white sugar with coloring. Please don't become a guinea pig for another poorly-tested toxic sweetener only to find out years from now that it contributed to the destruction of your health. These effects may or may not be a problem in long-term ingestion of sucralose by humans. Links to Mark Gold's huge aspartame site.