In a bowl place the drumsticks, mirin, ginger, salt, white pepper, celery salt and fennel powder. Mix together well. Cover and set aside.
Make the sauce by mixing 3 tablespoons gochujang and all of the other ingredients in a medium sized saucepan and cook over a low-medium heat until bubbling. Remove from heat and set aside
Mix the remaining 3 tablespoons of gochujang with the Kewpie mayo and place in a serving bowl.
Preheat the oven to 150°C/130°C fan. Heat the oil in a large saucepan or deep fryer to 175°C.
Remove the chicken from the marinade and place it in the corn starch and coat liberally. Fry the chicken in batches for 3-5 minutes or until golden. Remove and place on paper towel on a roasting tray and place in the oven. Repeat until all the drumsticks are cooked. Using a sieve or slotted spoon remove any debris. Fry the chicken again in several batches for 2 minutes or until deep brown. Return the chicken to oven. Reheat the sauce until bubbling. Place the chicken in a serving bowl and pour over the sauce. Serve with the gochujang mayo.