Trim excess fat from the chicken thighs and set aside. Mince the garlic and slice the ginger.
In a large pot, combine soy sauce, water, brown sugar, garlic, and ginger. Stir well and bring to a gentle boil over medium heat.
Add the chicken thighs to the pot, making sure they are fully coated in the sauce. Reduce heat to medium-low and let it simmer for 25 to 30 minutes.
Continue cooking uncovered, turning the chicken occasionally, until the sauce thickens into a rich, glossy, caramelized glaze that coats the chicken.