Here is a way to precook fresh takenoko:
Wash harvested takanoko and cut out the top edge and make a straight cut on leaves from the top to the bottom. Put them in a large pot and pour enough water to cover. Add 1/2 - 1 cup of nuka (rice bran) and a couple of togarashi (dried red chili pepper) and put on high heat. When it boils, turn down the heat to low and simmer for about one hour or until takenoko are softened. Stop the heat. When it cools down, drain takenoko and rinse them. Remove leaves and cut takenoko into desired size.