1. Cut off the top of the red pepper and scoop out the seeds. Soak the pepper in cold water for 1 hour, then slice crosswise into very thin rings.
2. In a 1-quart enameled or stainless-steel saucepan, combine the square of kombu, dashi, vinegar, soy sauce and sugar, and mix together thoroughly.
3. Bring to a boil over high heat, add the salt and a few sprinkles of MSG, then remove the pan from the heat. Stir in the red-pepper rings, and cool to room temperature.
4. Pour into a 10- to 12-inch skillet enough vegetable oil to rise about 2 inches up the side of the skillet. Heat the oil over high heat until a light haze forms above it.
5. Dip the pieces of fish into the flour, shake off the excess, then fry for 30 seconds, or until the fish turns a light gold. Do not overcook.
6. Remove the fish with a slotted spoon or tongs, and drain on paper towels. Pour the previously prepared sauce into a large bowl, add the fried fish and let it marinate for 2 to 4 hours, uncovered, at room temperature.
7. Drain the fish, discard the sauce, and arrange 4 pieces of fish on each serving plate. Serve at room temperature as part of a Japanese meal, or as a first course.
