Combine koikuchi shoyu, mirin, sake, and sugar in a small saucepan. Bring to a gentle simmer over medium-low heat, stirring until the sugar dissolves. Remove from heat.
2
Add katsuobushi to the saucepan with the seasoned liquid. Stir gently to coat all the katsuobushi flakes evenly.
3
Let the katsuobushi steep in the liquid for 5 minutes, allowing it to absorb the flavors.
