01 - Rinse sushi rice under cold running water until the water runs completely clear. Transfer the rice and 2½ cups water to a medium saucepan, bring to a rolling boil, then cover with a tight-fitting lid. Reduce heat to low and simmer for 15 minutes. Remove from heat and let the rice steam, covered, for an additional 10 minutes without lifting the lid.
02 - In a small saucepan, combine rice vinegar, sugar, and salt over low heat, stirring until fully dissolved. Transfer the steamed rice to a wide, shallow bowl or hangiri. Drizzle the vinegar mixture over the rice while gently folding and fanning simultaneously to cool it to room temperature and achieve a glossy finish.
03 - Shred or cut the imitation crab sticks into thin strips. In a small bowl, toss the crab with Japanese mayonnaise until evenly coated. Set aside.
04 - Place a bamboo sushi rolling mat on your work surface and cover it tightly with plastic wrap. Lay one sheet of nori shiny side down onto the mat. Wet your hands in a small bowl of water, then spread approximately ½ cup of seasoned sushi rice evenly across the nori, leaving a ¾-inch border at the top edge.
05 - Sprinkle the rice surface evenly with tempura flakes and toasted sesame seeds. Carefully flip the nori sheet so the rice side faces down on the plastic-wrapped mat.
06 - Lay a horizontal line of the crab-mayonnaise mixture, sliced avocado, and julienned cucumber along the bottom edge of the nori, approximately 1 inch from the bottom.
07 - Using the bamboo mat as a guide, roll tightly from the bottom edge upward, tucking the fillings firmly inward as you go. Apply gentle even pressure along the length of the roll to shape it and seal the seam. Let the roll rest seam side down for 1 minute.
08 - Wipe a sharp knife with a damp cloth. Slice each roll into 6 even pieces, wiping and rewetting the blade between cuts for clean edges. Press gently to maintain shape.
09 - Sprinkle additional tempura flakes on top of each sliced piece for extra texture. Arrange on a serving platter alongside small dishes of soy sauce, pickled ginger, and wasabi paste.