Divide the sushi rice into 12 portions and shape each portion into quenelles or oblong balls with hands moistened in water. Peel the shrimp, leaving the tails on. Butterfly the shrimp (cut in half lengthwise without cutting all the way through), and unfold the shrimp so that it lays flat. Brush the shrimp with wasabi and place on the rice balls.
Shape the shrimp around the rice with the tail hanging over the edges. Press with your thumb so the rice retains its shape. Place the nigiri sushi, rice sides down on a plate and serve.