Place rice into a large, deep bowl. Fill with cold water and rub rice together with hands until water turns milky white. Pour off cloudy water, being careful not to pour out rice. Repeat 3 or 4 times until you can see rice through 3 inches of water.

Drain rice in a fine strainer, then place into a saucepan along with konbu and 3 cups water. Allow to stand for 30 minutes. Stir together rice vinegar, sugar, and salt until dissolved in a small bowl; set aside.

Cover, and bring rice to a boil over high heat, then reduce heat to low, and simmer for 15 minutes. Remove from heat and allow to stand, covered, for 5 minutes.

Scrape rice into a bowl; remove and discard konbu. Stir in vinegar mixture until well incorporated and no lumps of rice remain. Allow to cool at room temperature. For a shinier appearance, use an electric fan to cool rice rapidly.