PREPARATION OF SUSHI RICE:
In a small bowl, combine the sake vinegar, rice vinegar and sugar. Stir until the sugar is dissolved.
Pour the vinegar-sugar mixture into the Japanese rice. Mix until the mixture is completely absorbed by the rice.
MAKING THE MAKI:
On a flat surface, place the nori wrapper on top of the bamboo rolling mat.
Wet your fingers with water then spread the sushi rice evenly onto to the nori wrapper.
Place slices of salted eggs, onions, tomatoes and cucumbers on the bottom part of the nori wrapper.
Grab the edge of the mat closest to you, keeping the fillings in place with your fingers, and roll it into a tight cylinder, using the mat to shape the cylinder. Pull away the mat and set aside.
Trim the edge of the rolled sushi then cut the cylinder in half using a sharp knife.
Slice each half crosswise into 3 to 4 equal pieces.
Repeat steps 3-8 until all the sushi rice is consumed.
Serve with wasabi and soy sauce.