Put steak on a waxed paper-lined baking sheet. Freeze until just firm, about 1 hour.
Meanwhile, for sushi rice, rinse rice under cold running water, rubbing grains together with your fingers. Combine rice and water in a small saucepan. Bring to a boil; reduce heat to low. Simmer, covered, until tender and sticky, about 15 minutes. Remove from heat. Stir together vinegar, sugar, and salt in a small bowl. Stir into rice. Cover; let cool about 45 minutes.
Meanwhile, thinly slice steak across the grain into 24 (1/4-inch-thick) slices. Transfer steak to a zip-top bag set in a shallow dish.
Whisk together soy sauce, maple syrup, chili paste, and oil in a small bowl. Pour over steak in bag; seal bag. Chill at least 20 minutes or up to 2 hours.
For sauce, whisk together sour cream, lime zest, lime juice, and wasabi paste.
Shape rice with wet hands into 24 (1-tablespoon) oval-shaped portions. Drain steak; discard marinade. Put steak on a foil-lined baking sheet set on a wire rack. Char steak with a kitchen torch, turning once, until desired doneness, about 5 minutes for entire recipe. Put 1 steak piece on each rice portion. Sprinkle with furikake seasoning and serve with sauce.
