In 4 qt. slow cooker bowl combine chicken, soy sauce, brown sugar, rice vinegar, garlic, and ginger.
Stir well to make sure all ingredients are mixed together. Once mixed, push the chicken to it's immersed in the sauce as much as possible.
Place lid on. Cook until chicken is tender (High - about 4 hours : Low - 5-6 hours). If possible, stir at least once during cooking and push chicken down so it's immersed in the sauce again.
Optional: to thicken the sauce Once chicken is cooked: Make the corn starch slurry: mix cornstarch and cold water in small bowl. Stir the mixture so that all the cornstarch is completely dissolved, leaving no lumps. Quickly stir in the cornstarch slurry into the chicken mixture and combine well so that the cornstarch doesn't thicken and become lumpy. Continue to cook for about 5 minutes or until thickened.
Cut or shred the chicken to your preferred size.
Put the chicken back into the slow cooker with all the sauce.
Spoon the teriyaki chicken and sauce on rice, noodles or in a sandwich.