Asian grocers sell nori furikake, a salty, dried seasoning made with seaweed and sesame seeds. If you can't find it, simply omit. Light soy sauce, not to be confused with reduced-sodium (often labeled "lite"), is thinner and more subtly flavored than dark soy sauce. This mayonnaise dipping sauce goes well with fried foods. Kewpie is a Japanese mayonnaise and yuzu kosho is a hot Japanese paste. Both are available at Amazon.com
.To make chicken:
In a wide, shallow dish, whisk together sake, soy sauce, garlic, ginger, and mirin. Add chicken, cover, and refrigerate, turning occasionally, 6 to 8 hours. (You can also marinate overnight.)
Preheat oven to 350°. Remove chicken, pat dry, and roast on a greased baking sheet, flipping once, until just cooked through, about 20 minutes; let cool.
Pour oil into a large pot to reach a depth of 2 inches and heat over medium-high until oil registers 350° on a thermometer.
Meanwhile, put 1 cup all-purpose flour into a wide, shallow dish. In a large bowl, whisk together remaining 1 1/2 cups all-purpose flour, rice flour, furikake, salt, and baking soda. Add club soda and beaten egg; whisk to make a batter.
Dredge half the chicken pieces in flour, then dip in batter, shaking off any excess. Carefully drop chicken into oil and fry, turning once, until golden brown, 4 to 5 minutes; transfer to a paper-towel-lined plate to drain. Repeat with remaining chicken; garnish with furikake and serve hot.To make sauce:
Mix ingredients together. Serve as a dipping sauce for fried chicken.