Cut the chicken thighs into bite-sized pieces and pat them dry with paper towels.
Put the soy sauce, sake, mirin, ginger, and chicken into a large zip lock bag and massage the chicken until all pieces are coated with the marinade. Let sit in the fridge for at least 30 minutes to 1 hour. Remove from the fridge 30 minutes before frying.
Heat vegetable oil in a deep pot or pan to 320°F. The oil should have a 1 ¼ to 1 ½ inch depth.
Drain excess marinade from the chicken and place it on paper towels to remove excess liquid, then put them in a bowl.
Sprinkle the cornstarch and toss the chicken to coat every side with it.
Fry in small batches for 2.5-3 minutes, adding one piece of chicken at a time. You might have to move the pieces around to make sure they don’t stick to the bottom of the pot.
Remove chicken pieces from the oil and allow them to rest for 3-4 minutes on paper towels. Repeat until all chicken is fried and resting.
Increase the temperature of the oil to 374-392°F. Put the chicken pieces back into the oil in small batches. Fry for 30 seconds to 1 minute or until golden brown and crispy. Repeat with remaining chicken.
Serve immediately with shredded cabbage and sprigs of parsley to garnish.