For the marinade: Combine the chicken, garlic, soy sauce, vinegar and scallions in a bowl, and mix thoroughly. Marinate the chicken overnight for at least 12 hours.
For the slaw: Shred the cabbage, and then combine the shredded cabbage with the vinegar, pepper, salt and sugar until the cabbage is thoroughly coated.
For the chicken: Remove the chicken from the marinade, and coat completely in the cornstarch. Rest the chicken in the cornstarch for 20 minutes to ensure it adheres completely.
Heat the oil over medium heat until a deep-frying thermometer inserted in the oil reaches 350 degrees F. Fry the chicken until it floats to the top and reaches an internal temperature of 165 degrees F.
Drain the chicken on a wire rack set over a sheet try or on paper towels, and then season with salt and togarashi.
Serve with the cabbage slaw and garnish with the scallions and kecap manis.