Slice green onions thinly. Peel and grate ginger root. Set aside.
Cut Tofu into 4 pieces. Wrap with layers of paper towels and remove moisture. Coat Tofu with potato starch.
Heat a frying pan with oil at medium heat. Put Tofu in the pan, and cook while slowly turning, until all the surfaces are lightly browned.
Add Soy Sauce, Sake, Mirin, and water, and cook for a couple of minutes, turning a few times. Reduce the sauce slightly.
Top with green onions, ginger, and Katsuobushi. Serve hot.