Roast the nori with the shiny, smooth side up over a flame. Hold it 10 to 12 inches above the flame, and rotate it until the color changes from black to green (about 3 to 5 seconds). Fold the nori in half and tear along the fold. Then fold in half again and tear so that you have 4 equal-sized pieces of nori (about 3-inches square).

Wet your hands slightly in a dish of water. Take half of the rice in your hands and form into a ball, as if your were making a snowball, or into a triangle by cupping your hands into a "V" shape. Pack the rice to form a solid ball or triangle.

Using your index finger, press a hole into the center of the ball, and place a piece of the umeboshi plum inside. Then pack the rice again to close the hole.

Place one square of the toasted nori on the rice ball. Wet your hands slightly and press the nori onto the ball so that it sticks. Take another square of toasted nori and place it on the other, uncovered side. Wet your fingers and press the ball again so that the nori sticks. The rice ball should be completely covered with nori.

Repeat until the rice, nori, and umeboshi are used up.