Katsuobushi is a type of dried, fermented and smoked skipjack tuna. it is used as a garnish for various dishes in Japanese cuisine, such as okonomiyaki and takoyaki. it is also used to make dashi, a Japanese vegetable broth. katsuobushi is made by a process called itokezuri, which involves steaming the tuna, filleting it and soaking it in salt and koji for several months. the marinated fish is then smoked and dried for several months before being ready to use.