Preheat oven to 350 degrees. Spray a muffin tin with nonstick spray.
Prepare rice: In a small bowl, combine rice vinegar, sugar, and salt. Pour mixture over cooked rice and stir to combine. Set aside.
Prepare imitation crab mixture: In a small bowl, combine crab, mayonnaise, salt, pepper, and cream cheese. Mix with fork, shredding imitation crab at the same time.
Place about 1/4 cup of rice onto nori sheet. Press down and place in muffin tin, molding to fit.
Add about 3 tablespoons of imitation crab filling to top of sushi cupcake. Bake for 15 minutes, or until golden brown.
Allow sushi cupcake to cool before handling and adding toppings. Serve & enjoy!