Place the rice in a large bowl and fill with cold water. Stir the rice to remove any particles. Pour off water and continue to rinse with more cold water until the water runs clear.
To use rice cooker, add the rice to the rice cooker bowl. Pour in 3 cups water. Remove 2 tablespoons water and add 2 tablespoons sake. Add the piece of kombu. Let sit for 30 minutes before turning on rice cooker. If your rice cooker has a sushi setting, use it.
If you do not have a rice cooker, place ingredients above in a heavy saucepan and let sit for 30 minutes. Cover the saucepan and place over medium high heat to bring to a boil. Immediately when it comes to a boil, reduce heat to low and cook until water has dissolved and the rice begins to crackle. Remove from heat and let sit for 5 minutes.
While the rice cooks, combine the rice vinegar, sugar, and salt in a small bowl. Microwave for a minute and stir to dissolve the sugar and salt.
Remove the kombu from the cooked rice and pour the rice into Hangiri (large wooden tub) or a large casserole dish. Gently sprinkle the rice vinegar mixture over the rice and carefully fold the rice with a fan directed at the dish on a low setting or fanning the mixture with a fan or piece of cardboard with your other hand. Continue to fold until the rice cools. Cover with a damp cloth and set aside. Do not refrigerate.