Rinse the sushi rice thoroughly under cold water until the water runs clear. This removes excess starch, ensuring the rice cooks properly. Cook the rinsed rice with water in a rice cooker or on the stovetop according to package instructions.

While the rice cooks, combine the seasoned rice vinegar, sugar, and salt in a small saucepan. Heat over low heat, stirring, until the sugar and salt dissolve. Once the rice is cooked, transfer it to a large mixing bowl and gently fold in the vinegar mixture. Be careful not to mash the rice. Add the toasted sesame seeds and mix gently. Set aside.

Chop the imitation crab meat into small pieces, or pulse it in a food processor for a finer texture. In a mixing bowl, combine the chopped crab with Kewpie mayonnaise, sriracha (adjusting to taste), and the beaten egg. Mix thoroughly until well combined.

Preheat the oven to 350°F (175°C). Grease a baking dish with sesame oil or cooking spray. Spread the seasoned sushi rice evenly across the bottom of the dish. Sprinkle a generous layer of furikake seasoning over the rice.

Spread the crab mixture evenly over the rice layer, smoothing it out with a spatula. Sprinkle another layer of furikake on top, and garnish with black sesame seeds if desired.

In a small bowl, mix the remaining Kewpie mayonnaise with sriracha to create a spicy sauce. Use a spoon or a piping bag to drizzle the sauce over the top of the crab layer in your preferred pattern.

Place the assembled dish in the preheated oven and bake for approximately 25 minutes, or until the top is golden and bubbling. Remove from the oven and let it cool slightly.

Garnish with sliced cucumbers and chopped green onions. Serve the sushi bake hot, accompanied by nori sheets for scooping.