Cut the chicken thighs into bite-sized pieces (about 1.5-inch cubes).
Place the chicken in a bowl and season with soy sauce, sake (or mirin), grated ginger, minced garlic, salt, and black pepper.
Mix well and let the chicken marinate for at least 30 minutes (or up to 2 hours for deeper flavor).
Place the potato starch in a shallow dish.
Remove the chicken from the marinade, letting the excess drip off.
Dredge each piece in the potato starch, ensuring an even coating.
In a deep frying pan or wok, heat about 2 inches of oil to 350°F (175°C).
Test the oil by dropping in a small piece of coated chicken—if it sizzles immediately, the oil is ready.
Fry the chicken in batches to avoid overcrowding. Cook for about 3-4 minutes per side, until golden brown and crispy.
Remove the chicken and drain on a wire rack or paper towels.
Increase the oil temperature to 375°F (190°C).
Fry the chicken again for 1-2 minutes to make it extra crispy.
Serve the karaage hot with lemon wedges, Japanese mayo, and shredded cabbage.
Enjoy with rice or your favorite dipping sauce.