Prepare the Chicken:
Cut chicken into bite-sized pieces, keeping the skin intact.
Marinate:
In a bowl, whisk together soy sauce, sake, ginger, and white pepper.
Add chicken and toss to coat. Cover and refrigerate for at least 2 hours or overnight.
Preheat Oil:
Line a tray with a rack or paper towels.
Heat oil in a wok or heavy pot to 325°F (160°C).
Coat and Fry:
Place potato starch in a shallow dish.
Dredge marinated chicken pieces in starch, shaking off excess.
Fry in small batches, turning occasionally, until light golden brown (about 3-4 minutes).
Transfer to the prepared tray.
Double Fry for Extra Crispiness:
Increase oil temperature to 375°F (190°C).
Return all chicken to the hot oil and fry for 2 minutes until crispy.
Drain and let cool slightly.
Serve:
Enjoy with steamed rice, vegetables, and lemon wedges.