In a large mixing bowl, whisk together mochiko flour, potato starch, eggs, sugar, soy sauce, mirin, chopped scallions, minced garlic, and grated ginger until smooth.

Cut the chicken thighs into strips and add them to the marinade, ensuring each piece is coated. Cover and refrigerate for at least 4 hours or ideally overnight.

In a Dutch oven, heat enough vegetable oil to submerge the chicken to 350°F (175°C), ensuring the oil is shimmering but not smoking.

Carefully add chicken pieces to the hot oil, cooking in batches for about 4-5 minutes or until golden brown and crispy. Transfer to a wire rack to drain excess oil.

Drizzle the fried chicken with spicy mayo and sprinkle with furikake before serving.