Place rice in a fine mesh strainer and rinse under cold water until water runs clear.

Transfer rice to a medium saucepan along with 2 1/4 cups water. Bring to a full boil, then reduce heat to low, cover, and simmer for 15 minutes. Remove from heat, keep covered, and let rest for 10 minutes.

In a small saucepan, combine 4 Tbsp of the vinegar with the sugar and salt. Heat over medium heat, cooking and whisking until sugar has dissolved. Remove from heat and let cool while rice is resting, then pour over rice and toss to evenly coat.

In a small mixing bowl, whisk together mayonnaise and sriracha. Transfer to a sandwich size resealable bag and set aside.

In a small mixing bowl, whisk together soy sauce and remaining 1 Tbsp vinegar and set aside.

In a large mixing bowl, gently toss together crab meat, cucumber, carrots, nori, ginger, and avocado or keep them separate and divide into sections over rice in serving bowls.

Divide prepared rice among 4 or 5 bowls and top with crab mixture.

Spoon soy sauce mixture over each serving. Cut a small tip from one corner of the resealable bag and drizzle sriracha mayo over each serving. Serve shortly after preparing.