Step 1: Place the short-grain sushi rice in a large bowl and cover with cold water. Swirl gently for 30 seconds until the water turns cloudy. Drain and repeat 5-7 times until the water runs mostly clear.
Step 2: Drain the washed rice thoroughly using a fine-mesh sieve and let it rest for 30-60 minutes to absorb any remaining surface water evenly.
Step 3: Transfer the drained rice to a heavy-bottomed pot with a tight-fitting lid. Add 2 cups of cold water.
Step 4: Bring the water to a rolling boil over medium-high heat. Once boiling, immediately reduce heat to the lowest setting, cover tightly, and simmer for 15 minutes.
Step 5: Remove the pot from the heat. Keep the lid on and let the rice steam undisturbed for another 10-15 minutes.
Step 6: While the rice rests, prepare the seasoning: In a small saucepan, combine unseasoned rice vinegar, granulated sugar, and fine sea salt. Heat over low heat, stirring constantly, until sugar and salt are completely dissolved. Do not boil. Let cool slightly.
Step 7: Transfer the cooked rice to a large, wide, non-metallic bowl or a hangiri. Using a non-metallic spatula or wooden spoon, gently separate the grains.
Step 8: Gradually pour the cooled vinegar mixture over the rice while fanning it with a hand fan or cardboard. Gently fold and fan the rice until the seasoning is evenly distributed and the rice has cooled to room temperature.
Step 9: Cover the seasoned sushi rice with a damp cloth or plastic wrap to prevent it from drying out. Use immediately or within a few hours for the best texture and flavor.