Place a sieve over a bowl, add rice, and rinse it with water. Repeat this process several times, changing the water each time.
Soak the rinsed rice in water in a pot for at least 30 minutes.
Mix water (as specified in the recipe) and salt in another pot and bring it to a boil. Once boiling, add green peas and simmer over low heat for 5 minutes. After that, turn off the heat and let them cool down.
Transfer the green peas to a bowl. Do not discard the boiled water, as you will need it for the next step.
Discard the water in which the rice was soaked from the pot. Combine the drained rice with sake and the water that has been boiled with green peas (the amount specified in the recipe) in the pot.
Cover the pot and bring it to a boil. Once boiling, reduce the heat to low and continue cooking for 10 minutes, or slightly longer for larger quantities (11 minutes for 4 servings, 12 minutes for 6 servings).
Turn off the heat and let it steam for 10 minutes with the lid still on.
Mix the green peas into the cooked rice.