Place chicken thighs in a shallow dish. In a small bowl, mix together soy sauce, sake, sugar and ginger. Pour the mixture over the chicken.
Marinate for at least 30 minutes. Heat a skillet over medium-high heat and add the chicken with the marinade. Cook for about 8 minutes, or until cooked through.
Transfer to a cutting board and cut into thin slices.
Assemble the bento box with rice, vegetables and teriyaki chicken.
Serve with pickled ginger, seaweed salad and miso soup.