Miso shiru is a traditional Japanese soup consisting of a stock called "dashi" into which softened miso paste is mixed.
Many ingredients are added depending on regional and seasonal recipes, and personal preference. The most common dashi soup stocks for miso soup are made of niboshi (dried baby sardines), kombu (dried kelp), katsuobushi (thin shavings of dried and smoked bonito, aka skipjack tuna), or hoshi-shiitake (dried shiitake). The kombu can also be used in combination with katsuobushi or hoshi-shiitake.
The kelp and/or shiitake dashi serve as a vegetarian soup stock.