Katsuobushi

Katsuobushi is simmered, smoked and fermented skipjack tuna (Katsuwonus pelamis, sometimes referred to as bonito). It is also known as bonito flakes or broadly as okaka (おかか). Shaved katsuobushi and dried kelp—kombu—are the main ingredients of dashi, a broth that forms the basis of many soups (such as miso) and sauces (e.g., soba no tsukejiru) in Japanese cuisine. Katsuobushi's distinct umami taste comes from its high inosinic acid content. Traditionally made katsuobushi, known as karebushi, is deliberately fermented with Aspergillus glaucus fungus in order to reduce moisture. Katsuobushi has also been shown to impart kokumi (a term translated as "heartiness").

Source: Wikipedia