Trim excess fat and cut the Chicken Thighs into bite-sized pieces (about 1–1½ inches).
In a bowl, combine the Soy Sauce, Sake, Mirin and Sugar with finely minced Garlic and grated Ginger to make the marinade; stir until the sugar dissolves.
Add the chicken to the marinade, mix well to coat, cover and refrigerate for 20–30 minutes (or up to a few hours for deeper flavor).
Place the Potato Starch in a shallow dish. Remove the chicken from the marinade, letting excess drip off, and dredge each piece in the starch so it is evenly coated; shake off any excess.
Heat enough Neutral Oil in a heavy-bottomed pan or deep fryer to come about 1–2 inches up the side and bring to medium-high heat (around 170°C / 340°F).
Fry the chicken in batches without crowding for about 3–4 minutes until the coating sets and pieces are just cooked through; transfer to a wire rack or paper towel to rest for a few minutes.
Raise the oil temperature to slightly higher (about 190°C / 375°F) and return the chicken in batches for a quick second fry — 1–2 minutes — until deeply golden and extra-crisp.
Drain briefly, then serve immediately with wedges of Lemon to squeeze over the hot karaage.
