Prepare the chicken thighs: Remove the bones from the chicken thighs if needed. Trim extra fat and tendons. Flatten the chicken thighs slightly for even cooking.
Season the chicken: Lay the chicken thighs on a cutting board and season both sides with salt and pepper.
Coat with corn starch: Rub about 2 tablespoons of corn starch on the meat side only, not the skin side, to help absorb salt and create crispiness.
Heat the pan and cook chicken skin side down: Heat 1 tablespoon of oil in a pan over medium heat. Place chicken thighs skin side down and cook for about 4 minutes until skin is crispy and golden.
Flip and cook meat side: Flip the chicken thighs and cook the meat side for about 4 minutes on medium heat without moving them to avoid sticking.
Flip back to skin side: Flip chicken thighs back to skin side and cook for another 4 minutes on medium heat to brown the skin further.
Prepare teriyaki sauce: While chicken cooks, mix 2 tablespoons soy sauce, 2 tablespoons mirin, 2 tablespoons cooking sake, and 1 tablespoon sugar in a bowl until sugar dissolves.
Add sauce and simmer: Pour the teriyaki sauce over the chicken in the pan. Lower heat and cook for about 5 minutes, flipping occasionally, until sauce reduces and caramelizes on the chicken.
Serve: Cut the chicken into bite-sized pieces. Serve over white rice with steamed vegetables and garnish with toasted sesame seeds. Optionally add salad and dressing.