Put 4 ounces steamed rice on a square of plastic wrap. Make a hollow in the center of the steamed rice and put a pickled plum there.
Wrap the steamed rice in the plastic wrap and press into desired shape (triangular, ball or cylindrical).
Remove the plastic wrap and sprinkle 1/3 to 1/2 teaspoon salt over the whole rice ball.
Wrap the toasted dried laver (nori) around the rice ball. For triangle and ball shape, use 3 1/3 in. × 7 in. size. For cylindrical shape, use 1 1/2 in. × 4 1/3 in. size.
Rice ball is often used in box lunches for a picnic. Umeboshi is the most standard ingredient of rice balls and this rice ball is delicious.