Rinse rice bag under cold water to remove starch. Prepare rice according to package directions.

In small saucepan over medium-low heat, heat rice vinegar, sugar and salt until sugar and salt have dissolved, about 1 minute. Set aside.

In small bowl, mix mayonnaise, Sriracha sauce and sesame oil. Set aside.

Transfer cooked rice onto large baking sheet. Drizzle half the vinegar mixture over rice, turning until all rice is fully coated. Taste and add more vinegar mixture, if desired. Spread rice into thin layer and cool to room temperature. Sprinkle sesame seeds on top.

Lay down one sushi nori sheet. Spread layer of rice on it. Place half the carrots and cucumbers on rice. Place crab and shrimp on top.

Place another sushi nori sheet just under first one and roll. Repeat with remaining sushi nori sheets, rice, carrots, cucumbers, crab and shrimp. Wrap both burritos in plastic wrap. Let rest 10 minutes.

Slice burritos in half and serve with spicy mayo.