Wash the rice thoroughly until the water remains clear. Bring rice and 75 ml water to the boil in a closed pot. Turn off the heat and let the rice swell for 20 minutes. Remove the pot from the heat and let the rice steam for another 20 minutes in the open pot. Season rice with vinegar, salt and sugar.
Cut seaweed leaves crosswise into eight strips. Squeeze some rice into a square shape. Place them on the work surface and wrap a strip of seaweed around each one, pressing them together roundly and letting some of the seaweed protrude at the top. Rinse caviar briefly in ice-cold water and drain. Immediately before serving, add one teaspoonful of caviar to each rice