01 - Pound chicken thighs to even 1/4-inch thickness. Season both sides generously with salt and pepper, ensuring full coverage.
02 - Arrange three shallow dishes: flour in the first, beaten egg whisked with milk in the second, panko breadcrumbs in the third.
03 - Dredge each thigh thoroughly in flour, shaking off excess. Dip into egg mixture, allowing excess to drip off. Press firmly into panko, coating completely and shaking off loose crumbs.
04 - Heat 1/2 inch vegetable oil in skillet over medium heat to 350°F. Fry chicken until golden brown and cooked through, approximately 3-4 minutes per side. Transfer to paper towel-lined rack to drain. Slice into musubi-width strips.
05 - Whisk rice vinegar, sugar, and salt until dissolved. Gently fold into warm rice, taking care not to mash grains. Allow to cool slightly until handleable.
06 - Whisk tonkatsu sauce, soy sauce, and honey in small bowl until smooth and fully incorporated.
07 - Lay plastic wrap on flat surface. Place halved nori sheet shiny side down. With damp hands, press approximately 1/4 cup seasoned rice into compact rectangular shape centered on nori. Sprinkle with furikake if desired.
08 - Place chicken katsu slice over rice base. Drizzle lightly with prepared sauce. Top with thin layer of rice, pressing gently to adhere.
09 - Fold nori tightly around filling, using plastic wrap to compress into uniform rectangular block. Press firmly to ensure structure holds together. Let rest 2-3 minutes for nori to soften and seal.
10 - Remove plastic wrap. Slice musubi in half horizontally if desired. Serve immediately with extra sauce on the side, or wrap tightly for portable meal.