Steps:

1. 1 For the Nanbansu Marinade and Dip: In a small saucepan, combine soy sauce, vinegar, mirin, and sugar and cook over medium heat, stirring, until the sugar is dissolved. Nanbansu will keep, covered, in the refrigerator for up to 1 month.
2. 2 Place chicken meat in a 1-gallon zipper-lock bag (if using breast and thigh meat together, place each in a separate bag). Pour 2/3 cup marinade into the bag (or 1/3 cup into each bag), press out the air, and seal. Let marinate 8 hours.
3. 3 Soak wooden skewers in water for at least 30 minutes (to prevent them from burning up on the grill). Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and spread the coals evenly over half of coal grate. Alternatively, set half the burners of a gas grill to high heat. Set cooking grate in place, cover grill, and allow to preheat for 5 minutes. Clean and oil the grilling grate.
4. 4 Meanwhile, thread 5 to 6 pieces of chicken (keeping breast and thigh meat separate) onto each skewer, pushing the pieces together so that they’re touching. (This will keep the meat from drying out, but will ensure that the exteriors get crispy.)
5. 5 Grill chicken skewers over high heat, turning frequently, until well browned outside and cooked through on the inside, about 10 minutes total. If chicken begins to burn at any point, move to cooler side of grill to finish cooking.
6. 6 Serve chicken skewers with the remaining nanbansu on the side for dipping. If you like, you can also sprinkle some shichimi togarashi (Japanese chili blend) onto the skewers or mix a little yuzu kosho into the nanbansu dipping sauce for some extra flavor and heat.