Hon Dashi fish broth powder
Dashi is the essential ingredient that gives Japanese food it's unique Japanese flavor, which is the taste that my friend Vic Serbe calls "that dead, rotting fish flavor."
My grandmother had big clumps of moldy seaweed and strings of dried fish hanging in her kitchen which she used to make her dashi stock from scratch. The white mold on the seaweed and fish contributes to the "Japanese" taste.
These days, I just use the instant fish powder like this Hondashi brand. It's like a fish boullion -- mix it in hot water for miso and noodle soups and add as flavoring to other Japanese dishes such as katusdon.