Combine the shoyu, brown sugar, rice vinegar, garlic, ginger, and sesame oil in a bowl.
Place the chicken thighs in a large resealable bag and pour the marinade over them.
Seal the bag and refrigerate for at least 2 hours, preferably overnight.
Preheat your oven to 375°F (190°C).
Remove the chicken from the marinade and place it in a baking dish.
Bake the chicken for 30–35 minutes, basting halfway through with remaining marinade.
Once the chicken is fully cooked, let it rest for 5 minutes before serving.
Garnish with sliced green onions before serving, if desired.
