01 - In a large mixing bowl, combine the soy sauce, mirin, honey, brown sugar, rice vinegar, minced garlic, grated ginger, and sesame oil. Whisk until the honey and sugar are fully dissolved and the mixture is smooth.
02 - Add the chicken thighs to the bowl and turn each piece to coat evenly in the marinade. Cover and refrigerate for at least 30 minutes, or up to overnight for deeper flavor penetration.
03 - Preheat the oven to 400°F. Line a rimmed baking sheet with parchment paper or aluminum foil for easier cleanup.
04 - Remove the chicken thighs from the marinade, shaking off excess. Reserve all remaining marinade liquid. Place the thighs skin-side up on the prepared baking sheet, spacing them at least 1 inch apart.
05 - Roast the chicken for 35 to 40 minutes. After the first 20 minutes, baste the thighs generously with the reserved marinade using a basting brush. Continue roasting until the internal temperature reaches 165°F at the thickest part and the skin is golden and caramelized.
06 - While the chicken roasts, pour the remaining marinade into a small saucepan and bring to a rolling boil over medium-high heat. If a thicker glaze is desired, dissolve the cornstarch in cold water and whisk it into the boiling sauce. Simmer for 3 to 5 minutes, stirring occasionally, until the sauce is glossy and coats the back of a spoon.
07 - Transfer the roasted chicken thighs to a warm serving platter. Drizzle with the thickened teriyaki sauce and garnish with sliced green onions and toasted sesame seeds. Serve immediately.