Kusaya, which literally translates as “smells bad”, is a type of preserved dried fish.
During the Edo period, when salt was much more scarce, the people of Japan’s remote Izu Islands would save salt by preserving the fish they caught in a salty soup (kusaya-eki). The fish would then be laid out to dry in the sun.
When bigger catches came in, the same solution would be used salt to preserve multiple batches of fish. Although odorous, the smelly fish it produced came to be highly valued, and the same batch of kusaya-eki can be used for centuries, increasing in flavour and odour over time.