To Make the Dashi
Start by adding the water and kombu to a saucepan and bringing to a boil.
When the water is boiling, add the bonito flakes and simmer for 10-15 minutes.
Remove the saucepan from the heat and strain the water.
Combine the marinade ingredients and add the cut fish to marinade for at least 10 mins.
To Serve
Spoon rice in to a large bowl and place the marinaded fish on top. Sprinkle with the seaweed and serve with soy sauce, wasabi and the rest of the dashi.