Wash rice well, drain, and set aside. Wash oysters gently in salted water, and pat dry. Cut ginger root into thin skinny pieces.
In a pot, add water, salt, Soy Sauce, Sake, and Mirin. Let it boil, then add oysters and cook 3 minutes at medium heat. Remove oysters from the liquid.
Put rice in the bowl of a rice cooker. Add enough seasoned liquid to rice to reach the line for 2 cups of rice. Cook like white rice.
After the rice is done, add cooked oysters to rice and leave for 10 minutes. Then mix and serve.