1 cup water
3/4 cup soy sauce
1/4 cup packed light brown sugar
1/4 cup mirin
1/4 tsp freshly ground black pepper
1 (3-inch) piece fresh ginger
4 medium scallions
8 bone-in, skin-on chicken thighs
Cooked white rice, preferably short grain, for serving
Place water, soy sauce), brown sugar, mirin, and black pepper in a large pot or Dutch oven. Bring to a simmer over medium-high heat, stirring until the sugar is dissolved.
Meanwhile, prepare the following, adding each to the pot as you complete it: Smash a 3-inch piece of ginger with the flat side of a knife. Halve 4 medium scallions.
Add 8 bone-in, skin-on chicken thighs to the pot skin-side down in an even layer (they can overlap). Cover and reduce the heat to medium-low. Simmer for 30 minutes.
Uncover and flip the chicken thighs so that they are skin-side up, arranging them into a single layer. Adjust the heat as needed to maintain a simmer so that the sauce bubbles between but not up and over the pieces of chicken. Simmer uncovered until the chicken is tender, about 30 minutes more.
Transfer the chicken to a serving platter. Spoon off any fat from the surface of the sauce. Serve the chicken and sauce with cooked white rice.