Mix flour, dashi soup, and eggs in a bowl to make batter. Thickness of the batter should be like potage soup. Put oil inside cups of a takoyaki grill pan. Pour batter into the cups to the full. Put octopus, red ginger, and green onion in each hole. Grill takoyaki balls, turning with a pick. When takoyaki become rounds and brown, remove them from the pan and place in a plate. Put sauce and mayonnaise on takoyaki and sprinkle bonito flakes and aonori on the top.