Trim any excess fat and cut the chicken thighs into 2-inch strips; place the strips in a large bowl.
In a separate bowl, whisk together the beaten eggs, mochiko (sweet rice) flour, cornstarch, soy sauce, granulated sugar, sesame seeds, grated garlic, salt, and chopped green onions until smooth.
Pour the marinade over the chicken and toss until every piece is evenly coated. Cover and refrigerate for at least 4 hours or overnight.
When ready to fry, heat about 1 1/2 cups neutral oil in a deep skillet or Dutch oven to 325°F (medium heat).
Working in batches, add the marinated chicken pieces to the hot oil and fry until golden brown and cooked through, about 3–4 minutes per side (165°F internal temperature).
Remove the fried chicken with tongs and drain on a rack or paper towels; repeat with remaining chicken.
Arrange the crispy mochiko chicken on a platter, garnish with additional chopped green onions, and serve with steamed white rice if desired.