Combine soy sauce, mirin, sake, and sugar in a bowl and mix until the sugar dissolves to make the teriyaki sauce.

Place the chicken thigh fillets in the sauce and marinate for at least 30 minutes.

Cook the white rice by combining it with water in a pot, bringing to a boil, then covering and simmering on low heat for 18-20 minutes until the water is absorbed.

Preheat a nonstick pan over medium heat and cook the marinated chicken, skin side down, until golden brown.

Flip the chicken and pour the remaining sauce over it, cooking until the sauce thickens and coats the chicken.

Toast sesame seeds in a dry pan over low heat until they are golden brown.

Chop the green onions for garnish.

For the miso soup: bring dashi stock to a gentle simmer in a pot.

Add miso paste, tofu cubes, and dried seaweed to the dashi stock, stirring until the miso paste dissolves and the tofu is warmed through.

Serve the chicken teriyaki garnished with toasted sesame seeds and chopped green onions, accompanied by steamed rice and miso soup.