Pat 6 bone-in, skin-on chicken thighs completely dry with paper towels (5 minutes). Dry chicken ensures crispy skin, so don't skip this step. Season both sides generously with salt and black pepper. Checkpoint: Chicken should look dry with no moisture on the surface.

Heat 2 tablespoons vegetable oil in a large skillet (12-inch recommended) over medium-high heat for 2–3 minutes until the oil shimmers and moves easily around the pan. You should see wisps of heat rising from the oil. Checkpoint: Oil should shimmer and move like water.

Carefully place all 6 chicken thighs skin-side down in the hot oil (work in two batches if your skillet is smaller). Do not move them for 6–8 minutes. Listen for a gentle, steady sizzle—this means the skin is crisping. The skin should turn golden-brown and pull away slightly from the pan when ready. Checkpoint: Skin should be golden-brown and crispy; you should see brown bits on the pan bottom.

Using tongs, flip each chicken thigh carefully and cook skin-side up for 3 minutes more over medium-high heat. The underside should be lightly browned. Checkpoint: Bottom of thighs should have light golden-brown color.

While chicken cooks, combine in a small bowl: 1/2 cup soy sauce, 1/4 cup mirin, 2 tablespoons honey, 1 tablespoon rice vinegar, 3 minced garlic cloves, and 1 tablespoon minced fresh ginger. Stir until honey dissolves completely (1–2 minutes). Smell the mixture—it should be fragrant with garlic and ginger. Checkpoint: Honey is fully dissolved and mixture smells aromatic.

Reduce heat to medium (lower the flame slightly). Slowly pour the teriyaki mixture over the chicken thighs, being careful not to splash. The liquid should partially cover the chicken. Checkpoint: Mixture is poured and chicken is partially submerged.

Simmer for 10 minutes, turning chicken with tongs every 2–3 minutes (3–4 turns total). Each turn should coat the chicken in the glossy sauce. The sauce will bubble gently around the edges. Checkpoint: Chicken is coated in sauce and has cooked 10 minutes total.

In a small bowl, mix 1 tablespoon cornstarch with 2 tablespoons water, stirring until no lumps remain (1 minute). The mixture should look like thin cream. Checkpoint: Cornstarch and water are fully combined with no white lumps.

Slowly pour the cornstarch slurry into the simmering sauce while stirring gently with a wooden spoon or silicone spatula. Stir constantly for 3–5 minutes. The sauce will thicken gradually and turn glossy and dark. You'll see the consistency change from thin liquid to a glaze that clings to the chicken. Checkpoint: Sauce is glossy, thick enough to coat a spoon, and clings to the chicken.

Add 1/4 teaspoon red pepper flakes if you like mild heat; increase to 1/2 teaspoon for more spice. Stir well (30 seconds). Checkpoint: Red pepper flakes are evenly distributed.

Drizzle 1 teaspoon toasted sesame oil over the chicken and sauce, stirring gently to combine (30 seconds). You should smell a rich, nutty aroma. Checkpoint: Sesame oil is evenly mixed throughout.

Remove from heat. Scatter 2 sliced green onions (white and green parts) and 1 tablespoon sesame seeds over the top. Checkpoint: Garnish is evenly distributed and dish is ready to serve.

Let rest in the skillet for 2 minutes before serving. This allows the glaze to set slightly on the chicken.