Mirin is a kind of cooking alcohol made from mixing sticky mochi rice and rice koji. The sweet alcohol takes the edge off fish dishes, and the sweetness made from the starch reacting with the koji gives a rich taste and glaze. In addition, the sugar and alcohol content helps stop boiled food from breaking up. Although it’s not necessarily sweet, much of Japanese cooking uses sugar, but I prefer to use less sugar and use mirin instead.
Originally mirin was a kind of alcoholic drink. At New Year there is still the tradition of drinking “otose” to ward off bad spirits and bring long life. Otose is a drink made from mirin and herbs.