01 - Pound chicken thighs to even thickness. Season both sides thoroughly with salt and pepper.
02 - Dredge each thigh in flour, shaking off excess. Dip into beaten egg mixed with milk, then press firmly into panko breadcrumbs to coat completely.
03 - Heat 1/2 inch vegetable oil in skillet over medium heat. Fry chicken until golden brown and cooked through, approximately 3-4 minutes per side. Transfer to paper towels to drain. Slice into strips fitting musubi dimensions.
04 - Whisk rice vinegar, sugar, and salt in small bowl until dissolved. Gently fold mixture into warm rice. Allow to cool slightly while preparing other components.
05 - Combine tonkatsu sauce, soy sauce, and honey in small bowl. Whisk until smooth and well incorporated.
06 - Place plastic wrap on flat surface. Lay halved nori sheet shiny side down. With moistened hands, press approximately 1/4 cup rice into compact rectangular shape centered on nori.
07 - Sprinkle furikake over rice if desired. Top with chicken katsu slice and drizzle with small amount of prepared sauce. Add thin layer of rice, pressing gently to compact.
08 - Fold nori tightly around filling using plastic wrap to shape and compress musubi. Let rest 2-3 minutes for nori to soften and seal. Remove plastic wrap. Repeat with remaining ingredients.