Nashville hot chicken is defined by a paste, not a marinade. After the chicken is fried, it is brushed or dunked with a slurry of cayenne and other ground chiles suspended in a measure of the frying fat or hot oil, often loosened with a little brown sugar. That fat-borne spice paste is the whole identity of the sandwich. Because it is oil-based and applied to the finished crust rather than mixed into the brine, it lacquers the coating in a slick, brick-red coat that delivers heat as a direct, escalating burn instead of a background warmth. The pickle and the bread are not garnish; they are the only defense the build offers against it.
The craft is a controlled fight between the heat and everything around it. The chicken is brined for moisture and fried hot for a craggy, blistered crust, because a flat coating would not hold enough of the spiced oil to matter. The hot paste goes on while the crust is still hot so it sets into the surface rather than running off. Then the architecture of restraint: the fillet sits on plain white bread, soft and faintly sweet, chosen because it is starchy enough to blot oil and bland enough to be a firebreak. Flat dill pickle chips go on top, their vinegar and cold crunch the single sharpest counter to the rendered chile fat. The classic plating is two slices of white bread and pickles, nothing more, because anything richer would only add fuel. Eat it fast, before the oil works all the way through the bread.
The variations are mostly a heat scale rather than different sandwiches. Kitchens codify levels from a mild brush to a paste built to be a genuine dare, and the bun-and-slaw version trades the white bread for a soft roll and a creamy slaw that buys the eater more relief. It sits in the same family as the Buffalo chicken sandwich, a different regional answer to the same question of how to carry an aggressive sauce on a fried fillet, and that relative deserves its own article rather than being crowded in here.