Cook Sushi Rice: Rinse 2 cups of sushi rice thoroughly in cold water until the water runs clear. Combine the rinsed rice and 2 1/2 cups of water in a rice cooker or a pot with a lid. Cook according to instructions, then let sit, covered, for 10 minutes. In a separate bowl, mix 1/4 cup of rice vinegar, 2 tbsp of sugar, and 1 tsp of salt until dissolved; gently fold this mixture into the hot rice.
Make the Seafood Layer: In a bowl, combine 1/2 lb of chopped cooked shrimp, 1/2 lb of shredded imitation crab, 6 oz of softened cream cheese, 1/2 cup of Japanese mayonnaise, 2 tbsp of sriracha (if desired for spice), 1/2 cup of caramelized onions, and 2 tbsp of soy sauce. Mix until creamy and well combined. Preheat your oven to 375°F.
Assemble the Dish: Spread the cooked sushi rice evenly into a greased baking dish. Layer the creamy seafood mixture on top and sprinkle generously with furikake seasoning. Drizzle with additional Japanese mayo and sriracha.
Bake: Place the dish in the preheated oven and bake for 15-20 minutes until bubbly and slightly golden on top. Once done, let it cool for a few minutes before serving.
Serve: Scoop into nori sheets or serve directly from the dish, enjoying the delightful layers of flavors!