To marinate the chicken: Start by sifting 1/4 cup of cornstarch, sugar, and the Mochiko flour into a medium bowl, mixing them thoroughly. Next, take a small bowl and whisk together the gochujang, soy sauce, sake, ginger, eggs, and 2 tablespoons of water. Blend this wet mixture into your dry ingredients, whisking until smooth. Finally, add the chicken to the batter, cover it tightly, and let it rest in the refrigerator for at least 4 hours.

To make the aioli: Grab a small bowl and whisk the gochujang, sugar, and mayonnaise together until well blended. Cover the mixture tightly and keep it chilled in the refrigerator until it is time to use it.

To fry the chicken: Fill a heavy-bottomed saucepan with 2 inches of oil and bring the temperature to 325°F(160°C), checking it with a deep-fry thermometer. Meanwhile, grab a medium bowl and sift together the garlic salt, all-purpose flour, and the remaining 2 cups of cornstarch. Dredge the chicken thighs in this dry blend to coat them fully, tapping off any excess. Fry the chicken in the hot oil for about 3 minutes until perfectly golden-brown.