If you don’t have a rice cooker, you can simply use a pot with a lid to boil Japanese rice.
Here is the method for 2 cups of rice grains, which makes about 4 cups of cooked rice.
First, rinse the rice grains in a sieve/colander twice or thrice to clean. Don’t rub them, but simply swirl them around in the water. If the package says it’s been prewashed, this is not necessary.
Second, pour the rice into a pot, large enough to hold everything and some. Over the rice grains, pour 2.25 cups of water if you’re making sushi, or 2.75 cups of water for regular rice.
Cover with a lid and let it rest for about 45 minutes.
Heat the rice at medium heat until it boils, then turn it on high for 1 minute. Immediately after, drop the heat to the lowest temperature and cook for another 12-15 minutes. Don’t lift the lid, since the rice grains need every drop of moisture they can get!
After, remove from heat and let it stand for about 10-15 minutes.