Pat the sea bream fillets dry with paper towels, make shallow cuts on the skin side, and sprinkle with 1/4 tsp salt. Wrap in paper towels and refrigerate for 30 minutes.

Cut the green onion into thin diagonal slices.

In a pot, bring the dashi stock, sake, mirin, soy sauce, and 1/3 tsp salt to a boil. Add the sea bream and simmer over medium-low heat for about 3 minutes until cooked through. Remove the fish.

In a separate pot, boil water and cook the somen noodles according to the package instructions. Rinse under cold water and drain thoroughly.

Reheat the broth and add the somen noodles. Heat until warmed through, then add the sea bream and simmer briefly.