Step 1: Rinse the rice thoroughly. Place rice in a fine-mesh sieve or large bowl and rinse under cold running water, swirling with your hand, until the water runs mostly clear (5-7 changes). Drain well.
Step 2: Soak the rice. Transfer the rinsed rice to a heavy-bottomed pot with a tight-fitting lid. Add 2¼ cups cold water. Let soak for at least 30 minutes, up to 1 hour.
Step 3: Cook the rice. Bring rice and water to a boil over medium-high heat. Once boiling, reduce heat to the lowest setting, cover tightly, and simmer for 13-15 minutes. Do not lift the lid. Remove from heat and let rest, still covered, for 10 minutes.
Step 4: Prepare the sushi-zu (seasoning). While rice rests, combine ¼ cup rice vinegar, 2 tablespoons sugar, and 1 teaspoon salt in a small saucepan. Heat gently over low heat, stirring until sugar and salt are completely dissolved. Do not boil. Remove from heat and let cool slightly.
Step 5: Season the rice. Transfer cooked rice to a large, wide, non-metallic bowl (like glass or wooden hangiri). Gradually pour the cooled sushi-zu over the hot rice, using a cutting motion with a flat, non-metallic spatula or wooden spoon. Gently fold to evenly coat each grain without mashing.
Step 6: Cool and fan the rice. Continue to gently fold and spread the rice while fanning it simultaneously (with a hand fan or small desk fan). Fan until the rice cools to body temperature (around 98-100°F / 37-38°C) and develops a beautiful sheen. This takes 10-15 minutes.
Step 7: Cover and rest. Once cooled, cover the rice with a damp cloth or plastic wrap to prevent drying out. Use within a few hours for best results.