Place 2 1/4 cups of Japanese sushi rice in a large deep bowl.
Fill the bowl with cold water and rub the rice with your hands until the water turns milky white.
Carefully pour off the cloudy water, ensuring not to pour out the rice.
Repeat the process 3 or 4 times until you can see the rice through 3 inches of water.
Drain the rice using a fine strainer.
Place the drained rice, 1 piece of konbu kelp, and 3 cups of water in a saucepan.
Allow the rice mixture to stand for 30 minutes.
In a small bowl, stir together 1/4 cup of rice vinegar, 1/4 cup of white sugar, and 1 1/4 teaspoons of salt until dissolved.
Cover the saucepan and bring the rice to a boil over high heat.
Reduce the heat to low and simmer the rice for 15 minutes.
Remove the saucepan from heat and let it stand for 5 minutes.
Scrape the rice into a bowl and discard the konbu kelp.
Stir in the vinegar mixture until well incorporated and no lumps of rice remain.
Allow the sushi rice to cool at room temperature.
For a shinier appearance, use an electric fan to cool the rice rapidly.