In a mixing bowl, whisk together soy sauce, brown sugar, honey, rice vinegar, minced garlic, and ground ginger until the sugars dissolve completely.

Place the chicken thighs in a resealable plastic bag or a bowl, pouring half of the marinade over them. Seal the bag or cover the bowl, then refrigerate for 15 to 30 minutes.

Pour the remaining marinade into a saucepan and bring it to a boil over medium heat. Mix a cornstarch slurry with water and stir it into the saucepan. Let the sauce simmer for 10 to 12 minutes.

Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper or aluminum foil.

Remove chicken thighs from the marinade, discard the used marinade, and arrange the chicken on the prepared baking sheet. Brush generously with the thickened teriyaki sauce.

Bake boneless skinless thighs for 12 minutes, flip, brush with sauce, and bake for another 12 minutes. For bone-in thighs, bake for 15 minutes, turn, brush with sauce, and continue baking for another 15 minutes.

Broil under high heat for 1 to 3 minutes, keeping a close eye to prevent burning.

Let the chicken rest for 5 minutes after removing from the oven. Brush with more reserved sauce and serve.