Prepare rice according to package directions.
Place rice in non-metallic bowl; gently fold in rice vinegar, sugar and 1/2 tsp salt with a wooden spoon. Spread rice over the bottom of a large, shallow baking pan.
Cover rice with damp towel until needed (up to 3 hours), but do not chill.
Place a toothpick in the middle of the shrimp longways to prevent the curling of the shrimp during the cooking process. In a medium pot, filled halfway with water, add remaining salt, and boil for 3 minutes.
Immediately place shrimp in a bowl filled with water and ice to maintain color and texture. Remove toothpick. With a knife, cut the belly of shrimp lengthwise to butterfly the shrimp. Be careful not to cut all the way through.
Place a small amount of wasabi into the inside of each shrimp. Form the cooked rice into small balls and stuff them into the shrimp. Shape the shrimp around the rice with the tail hanging off the edge.
Serve rice-side down with soy sauce and pickled ginger.