Put karaage inside an onigirazu and you get the format's clearest argument for filling with structure. Japanese fried chicken, marinated in soy, ginger and garlic, dredged in potato starch and fried until the crust shatters, is the opposite of soft avocado or weeping tomato: it is the firmest thing the frame is ever asked to hold, and it changes the eating experience from a soft layered bite into something with real resistance at the center.
The construction is unchanged from the baseline. A square of nori on the diagonal, a flat bed of seasoned rice, the karaage laid across it, a second even layer of rice, the corners folded in to seal, a rest seam-side down, a clean halving to show the face. The chicken is the thing that needs handling. Whole karaage pieces are too tall and too round; pressed into a flat packet they bulge the nori and tear it, and the cut face becomes a lopsided lump. The reliable approach is to slice or lightly flatten the pieces into an even sheet so the band is continuous and the packet sits level. Most builds add a sauce that also defends the crust against the rice: Japanese mayonnaise, a sharp tartar, a sweet-soy glaze. A line of shredded cabbage between rice and chicken is common and useful, adding a cool crunch and a moisture barrier in one move.
The central tension is timing and crust. Karaage is at its best hot, when the coating is loud and the inside juicy; sealed cold into a rice packet it inevitably softens, the shatter fading toward chew. A good version accepts this and leans on the marinade flavor and the contrast between yielding rice and dense chicken rather than pretending the crust will stay crisp. Blotting excess frying oil is not optional, because oil wicks straight into rice and turns the band heavy and grey. The familiar faults are the format's usual ones sharpened by a bulky filling: clumped chicken that springs the nori, oil-soaked rice, a dry-knife cut that drags the coating into a smear instead of a clean rectangle.
Variations mostly play with the sauce and the cuisine it points to. Nanban style brings sweet vinegar and a tartar slick; a yuzu kosho mayonnaise adds citrus heat; a teriyaki-leaning glaze pushes it sweeter; a spicy Korean-style coating turns it sharp and red. Each of those reshapes the balance enough that it deserves its own article rather than being crowded in here.