Rinse the azuki beans.

Place the beans in a saucepan and add enough water to cover them (in addition to the measured water).

Bring to a boil over high heat.

Discard the cooking water to remove any bitterness.

Add the measured water and bring back to a boil over high heat.

Once it returns to a boil, reduce the heat to low, cover with the lid slightly ajar, and simmer for about 1 hour, until the beans are tender. Add more water if needed to keep them covered with liquid.

Once the beans mash easily, add the sugar in 2 to 3 additions and simmer briefly over low heat.

Add the salt to enhance the flavor.

Place the glutinous rice flour in a bowl, then add the water little by little, kneading until you have a soft dough (about the consistency of an earlobe).

Shape into balls of your desired size and press a slight indentation into the center of each one.

Drop the balls into boiling water. Once they rise to the surface, cook for about 1 minute more.

Remove the balls, transfer them to cold water to cool, then drain.

Add the shiratama balls to the zenzai and serve.