Toast the nori by waving it over a flame until it stiffens slightly, but be careful--it burns easily. Crumble into little pieces and set aside.
Combine all the sauce ingredients in a small saucepan and simmer for 30 seconds, stirring constantly.
Remove from the heat and cool to room temperature.
Beat the eggs in a large bowl.
Add the flour and water and continue beating until you have a batter the consistency of pancake batter.
Add the sake and salt.
Fold in the cabbage, carrots, and scallions. Be sure to mix the batter and vegetables together evenly. Each okonomiyaki will use 1/4 of this mixture.
Heat 1 tbsp. of the oil in a standard 10-inch skillet. Spoon 1/4 of the batter onto the hot skillet (like a pancake) making sure the vegetables are evenly distributed.
Then sprinkle 1/4 of the shrimp or meat of you choice on top.
Cook each side on medium heat for 2 minutes, until lightly browned. Reduce the heat to low and cook, covered, for another 5 minutes, occasionally turning and gently pressing the okonomiyaki with a spatula.
Prepare three more okonomiyaki as above. Keep the finished pancakes warm in a low oven while making the rest, or use two skillets and make two okonomiyaki at a time.
Serve hot with the sauce to taste--I recommend 1 tbsp. per okonomiyaki-- and top with about a tsp. of mayonnaise and a sprinkling of toasted nori.