01 - In a mixing bowl, whisk together soy sauce, mirin, sake, honey, brown sugar, rice vinegar, grated garlic, grated ginger, and toasted sesame oil until well combined.
02 - Add chicken thighs to the bowl, turning to coat evenly. Cover and refrigerate for at least 30 minutes, or up to 4 hours for deeper flavor penetration.
03 - Preheat a grill or grill pan to medium-high heat. Brush the grates with vegetable oil to prevent sticking.
04 - Remove chicken from the marinade, reserving the excess liquid. Grill thighs for 5–7 minutes per side until cooked through with a nicely charred exterior.
05 - Pour the reserved marinade into a small saucepan. Bring to a boil, then reduce heat and simmer for 3–4 minutes until the sauce thickens slightly.
06 - Brush the grilled chicken generously with the reduced sauce and transfer to a serving platter.
07 - Sprinkle with sesame seeds and sliced green onions. Serve immediately while hot.