Cook the rice: Rinse rice until water runs clear. Cook using a rice cooker or stovetop, then keep warm.
Prepare protein: Pound pork or chicken cutlets to ½-inch thickness. Season both sides with salt and pepper. For tofu, slice and pat dry.
Set up dredging station: Prepare three shallow bowls — one with flour, one with beaten eggs, and one with panko breadcrumbs.
Coat cutlets: Dredge each cutlet in flour, then dip into egg, and finally press into panko until fully coated. Let rest for 10 minutes.
Heat oil: In a deep skillet, heat oil to 165–175°C (330–350°F).
Fry: Cook cutlets 3–4 minutes per side until golden brown and crisp. Drain on a wire rack.
Make the sauce: Whisk all sauce ingredients in a small saucepan. Simmer 2–3 minutes, then cool.
Assemble bowls: Scoop rice into bowls, top with shredded cabbage, sliced katsu, and drizzle tonkatsu sauce. Garnish with scallions, sesame seeds, and a soft-boiled egg if desired.