A yakiniku onigirazu puts grilled, sauced beef inside the flat rice-and-nori frame, and that single choice makes it the richest, most dinner-like member of the family. Where the umeboshi version is austere and the tuna-mayo version is cool and mild, this one is warm in spirit and assertively savory: thin slices of beef cooked over heat and coated in a sweet-soy yakiniku sauce, packed as a broad layer so every bite reads as grilled meat over seasoned rice rather than a rice ball with a hidden center.
The construction is the shared one. A sheet of nori goes down shiny side toward the board, a thin even bed of warm rice is pressed onto the center, the beef is laid in a square that stops inside the edges, more rice caps it, and the four corners of seaweed fold in so the parcel rests seam side down before it is cut. With sauced beef the controlling problem is the sauce. Yakiniku glaze is sweet, dark, and loose, and if it is used wet it bleeds into the rice and softens the nori until the wrapper splits, so a careful build cooks the beef until the sauce reduces and clings, then lets the meat cool slightly before it goes in so steam does not turn the seaweed slack. The slices are kept thin and laid flat rather than mounded, which keeps the parcel pressable and the cut clean. Done well, the face shows a dark glossy band of beef threaded into pale rice inside a seaweed edge, and it eats savory and faintly sweet, the rice absorbing just enough sauce to taste seasoned while still holding its shape. Done badly, the sauce pools and soaks through, the rice will not compress, and the whole thing slumps the moment it is halved.
What the filling does inside the frame is shift the sandwich from snack toward meal. The beef and its sauce bring fat, sugar, and umami in a concentration the lighter fillings do not have, which is why this version is more satisfying on its own and why the rice layer earns its keep here as a counterweight rather than just a binder. It is best eaten while the beef is still close to fresh off the heat; held cold for hours it firms and loses the looseness that makes it good, unlike the tuna or pickled-plum builds that are designed to keep.
Variations stay inside the grilled-and-sauced logic: a bulgogi-style marinade, a gyudon sweet-onion simmer, karubi short rib in place of thin slices, or a kick of kimchi and lettuce folded in for crunch and acid against the richness. Each rebalances the meat, sauce, and rice enough that it deserves its own article rather than being crowded in here.