Place chicken in a glass, ceramic or other nonreactive dish, pour over the pickle juice and turn to coat. Cover and refrigerate for about 1 hour, turning several times to ensure the chicken pieces are flavored with the pickle juice.
Meanwhile, in another dish, whisk together the buttermilk and hot sauce. Season with salt and pepper.
Lift the chicken from the pickle juice and submerge it in the buttermilk marinade. Turn the chicken to coat, cover and refrigerate for at least 6 hours and 12 hours overnight.
To make the spice mix, combine the paprika, cayenne, brown sugar, garlic and onion powders, ginger and salt in a mixing bowl.
Lift the chicken pieces out of the marinade and lay them on a baking sheet. Sprinkle the spice mix over the chicken and let sit for 10 minutes to give the spice mix time to flavor the chicken.
Meanwhile, spread the flour and Karaage mix in a large shallow bowl or dish and stir to mix. Dip the chicken in the seasoned flour and coat on both sides. Shake the chicken to knock off some excess flour and evenly distribute it over the chicken. Refrigerate the coated chicken on the baking sheet for 30 minutes before frying.
Pour oil in a deep, heavy pot to a depth of 3 to 4 inches. Heat over medium-high heat until a deep-frying thermometer reaches 350°F.
When the oil reaches the desired temperature, use tongs to put the chicken in the oil. Do not crowd the pan—you may have to fry the chicken in batches. Turn the chicken several times to brown on all sides. Once lightly browned, let the pieces cook without turning for 18-20 minutes. Remove a piece from the frying oil and use an instant-read thermometer to make sure the chicken is cooked through (it will read 165°F when inserted into a meaty part of the chicken).
Once the chicken is cooked through, remove from the pot and set on a wire rack set over a baking sheet to drain. If frying in batches, let the oil regain its temperature before cooking the next batch.
Let the chicken cool for about 10 minutes before serving.