Whisk together soy sauce, mirin, sake, sugar, grated ginger, and minced garlic in a bowl to create the teriyaki sauce.

Pat the chicken thighs dry with paper towels, then place them in a shallow dish or a zip-top bag and pour half of the teriyaki sauce over the chicken, reserving the other half for later.

Heat a large skillet or frying pan over medium-high heat with a tablespoon of oil.

Once hot, add the chicken thighs to the skillet, skin-side down, and cook for about 5-7 minutes until the skin is golden brown and crispy.

Flip the chicken and cook for another 5-7 minutes on the other side until cooked through.

Remove the chicken from the skillet and set it aside.

Pour the reserved teriyaki sauce into the skillet and bring it to a simmer, cooking until it thickens slightly, about 2-3 minutes.

Slice the cooked chicken thighs and arrange them on serving plates.

Drizzle the thickened teriyaki sauce over the chicken.

Serve immediately with rice and steamed vegetables if desired.