Add rice to a large, deep bowl. Fill with cold water and rub rice together with hands until water turns milky white. Strain water from rice. Repeat 3 or 4 times until you can see rice through 3 inches of water. Strain rice from water. Add rice to a small saucepan. Stir in kombu and the 2 cups water.

Cover and bring rice to a boil over high heat, then reduce heat to low, and simmer until rice is tender and water is absorbed, about 15 minutes. Remove from heat and let stand, covered, 5 minutes. Remove and discard kombu.

Meanwhile, in a large bowl whisk together rice vinegar, sugar, and salt until dissolved. Add rice and stir until well incorporated and no lumps of rice remain. Allow to cool slightly before handling.

Line a square 8x8-inch baking pan with plastic wrap. Gently press the rice into the bottom of the dish and cover with additional plastic wrap. Refrigerate for at least 1 hour and up to 24 hours.

Remove rice from pan and cut into bite size rectangles (2x1-inch). In a deep, large skillet heat 3/4-inch of oil to 365°F. Working in batches, carefully place rice squares into the oil with a slotted spoon. Cook until golden brown and crispy, about 3 minutes each side. Remove from pan and place on a wire rack over a sheet pan to cool (inside of bite should still be a bit soft and chewy).

In a medium bowl mix together the tuna, mayonnaise, sriracha, soy sauce, sesame oil, and lime juice until incorporated. Serve with crispy rice bites and garnish as desired with sliced avocado, furikake, sesame seeds, green onions, and sliced jalapenos.