Place chicken in the bottom of the crockpot in an even layer.
In a bowl, whisk together soy sauce, brown sugar, garlic, ginger, rice vinegar, and sesame oil.
Pour the sauce evenly over the chicken.
Cover and cook on LOW for 4–5 hours or HIGH for 2–3 hours, until chicken is fully cooked and tender.
Remove chicken and shred with two forks, then return it to the crockpot.
In a small bowl, mix cornstarch with water to form a slurry. Stir into the crockpot.
Cover and cook on HIGH for 15–20 minutes, until the sauce thickens and coats the chicken.