Sashimi can be made with almost any fresh saltwater fish. Buy only sashimi-quality (''1-plus'') fish from a reliable fishmonger; don't use fish that is bruised or discolored, or that smells fishy; keep fish refrigerated; and slice just before serving.
6 tbsp. soy sauce
Niban-dashi (see Niban-Dashi recipe)
Yuzu (a type of citrus fruit), or lemon
1/4 lb. 1''-thick tuna fillet
1/4 lb. flounder fillet
1/4 lb. fillet cleaned, giant squid
1 chrysanthemum flower
1. For dipping sauce, mix soy sauce with niban-dashi to taste in a bowl, then divide between 4 small dishes, and season with the juice of yuzu or lemon zest.
2. Rinse tuna fillet in cold water, place on a very clean cutting board, and, using a sharp knife, cut into rectangular pieces, about 1/4'' thick. Rinse flounder fillet, place on board, and ''shave'' into thin slices (sharply angle knife, blade toward narrow end of fillet). Rinse giant squid. Score squid to tenderize, then julienne on the diagonal.
3. Place 2 slices tuna, 2 slices flounder, a pile of squid, and a dab of wasabi on each plate. Garnish with a wedge of yuzu or lemon, julienned daikon, and chrysanthemum flower. Serve with dipping sauce.