Cut chicken thighs into uniform pieces.
Mix soy sauce, sake, ginger, and garlic.
Add salt and pepper to marinade.
Marinate chicken for 30 minutes minimum.
Heat oil to 340°F (170°C).
Combine potato starch and flour thoroughly.
Coat marinated chicken in flour mixture.
Fry chicken pieces for 3-4 minutes.
Remove and drain on wire rack.
Increase oil temperature to 375°F (190°C).
Fry chicken again for 1-2 minutes.
Drain on paper towels immediately.
Serve hot for best texture.