In a large heavy-bottomed pot or Dutch oven, combine the soy sauce, sugar, water, minced ginger, garlic, and black pepper.
Place the pot over medium heat and stir until the sugar has completely dissolved and the mixture reaches a gentle simmer.
Add the chicken thighs to the pot, ensuring they are submerged in the braising liquid.
Reduce the heat to medium-low and simmer uncovered for 35 to 40 minutes, turning the chicken occasionally to ensure even coloring.
Continue cooking until the sauce has reduced slightly and the chicken is tender with an internal temperature of 165°F (74°C).
Remove from heat and garnish with sliced green onions.
Serve the chicken and sauce over steamed white rice.