Rinse sushi rice under cold water until clear, then cook according to package instructions. Let it rest for 10 minutes.

Combine rice vinegar, sugar, and salt in a saucepan and heat gently until dissolved. Let cool.

Fold sushi vinegar into cooled rice. Spread onto parchment-lined dish, press down, cover, and chill for 3 hours.

Finely dice sushi-grade ahi tuna and mix with sliced scallions in a bowl.

Whisk together Kewpie mayonnaise, Sriracha, and ponzu sauce in a bowl.

Cut chilled rice into 2-inch squares. Heat grapeseed oil in a skillet, fry rice squares until golden brown on each side.

Top each crispy rice piece with spicy tuna mixture and garnish with black sesame seeds and jalapeño slices. Serve warm.