Mix both cornflour and rice flour together with the water to make a fairly thin batter.
Heat a large heavy frying pan until very hot and add oil. Pour in the batter and cook for about 15 seconds until batter is half set before adding in the eggs.
When the eggs are almost set, make a hole in the centre by pushing the egg and batter mixture to the side of the pan. Pour in a little more oil and fry the garlic for a few seconds.
Mix, then season with soy sauce, sake and pepper. Add oysters and cook just long enough to heat through.
Garnish and serve immediately with fresh coriander leaves and spring onions.