Pat the chicken dry and cut into large pieces, about 2.5 inches each.
Whisk together the soy sauce, sake, mirin, ginger, and minced garlic. Add the chicken, toss to coat, and marinate in the fridge for at least 1 hour.
In a wide bowl, whisk the potato starch, cornstarch, and salt. Dredge each piece of chicken in the starch mixture, pressing to coat fully, and shake away any excess.
Heat 2 to 3 inches of oil to 325F. Fry the chicken in batches for 3 to 4 minutes, until pale golden and mostly cooked. Rest on a rack for 3 to 5 minutes.
Raise the oil to 375F. Fry the chicken again in batches for 1 to 2 minutes, until deep golden and crisp, to a minimum internal temperature of 165F. Drain on a rack and salt lightly right away.
Serve hot with lemon wedges and Kewpie mayo. Or serve it over white rice for a full meal. Enjoy!
