Rehydrate the koya tofu in hot water. If it's the type that doesn't need to be rehydrated, follow the instructions on the package. Make sure you use kouya tofu that doesn't have leavening agent in the ingredient list.
Slice the koya tofu in half lengthwise, then cut into half widthwise.
Combine the dashi soup stock and soy sauce, and simmer the kouya tofu in it to season. Boil down the dashi stock until it has completely evaporated. It's done if the dashi stock seeps out when you press down on the kouya tofu.
Dredge the koya tofu in flour, then with panko. If the koya tofu has dried out, coat in a flour slurry. Fry up in hot oil.
Story Behind this Recipe
A typical dish in the macrobiotic diet.
Use koya tofu with a chewy texture without a leavening agent. If you use the normal soft ones, these won't resemble chicken katsu when finished.