Prepare all your ingredients. Don't wash off the kombu, even if there is a white powdery substance on it because this gives it that intense umami flavor.
Using kitchen shears, cut the kombu in half, and then for each piece, cut some slits into the kombu until you reach the middle. About 3 slits per piece is enough to release more flavor into the broth.
In a medium pot, add the water and the kombu.
Heat the water on low to medium heat for approximately 10 minutes until it is almost at a boil.
Use a skimmer or spoon to remove any bubbly foam from the top of the dashi.
As the mixture starts to boil, remove the kombu pieces and throw them away.
Add all the katsuobushi and bring the mixture to a boil.
As soon as the dashi boils, turn down the heat and simmer for about 30-40 seconds. Turn off the heat.
Using a fine-mesh sieve, strain the dashi into a clean bowl or jar. The dashi stock is ready for use.