Very finely mince the shallot, and microplane the garlic. Combine all marinade ingredients in a mixing bowl, and whisk until the sugar has dissolved into the rest of the sauce.
Add to a large ziplock along with the kanpachi, seal the bag removing as much air as possible, and massage the marinade into the fish. Let marinate for at least 1 hour, or overnight. If marinating for any longer than an hour, make sure to keep it in the fridge, and then allow to come to room temperature before cooking.
Preheat the oven to 375°F. Line a baking sheet with foil, then place a rack on top. Spray the rack with a neutral-flavored cooking spray.
Take the fish out of the bag, and use your hands to scrape off as much of the marinade as possible. Lay the fish skin-side down on the prepared rack.
Place in the oven for 15-20 minutes, until the fish is cooked through and turning golden.
While the fish cooks, combine the glaze ingredients in a small pot and place over very low heat to warm and allow the ingredients to melt together. Stir, and do not bring to a simmer.
When the fish is done, carefully take it out of the oven and switch to the broiler. Make sure the oven rack is not directly below the broiler, but one level down, so that the fish doesn’t burn.
Brush the fish liberally with the glaze, then place under the broiler for about 3-5 minutes until brown. Take the fish out of the oven, and use a fish spatula to remove from the rack. The fish won’t slice like a classic pork char siu, but can be flaked or cut into portions.
