First marinade the chicken in some nihonshu (sake), some garlic powder and white pepper. Leave in the marinade for around half an hour.
Sift together equal parts of cornflour and plain flour. Season well with salt and white pepper.
To make the glaze, in a small saucepan add a few tablespoons of black vinegar, a tablespoon or so of soy and a tablespoon of sugar. Add a dash of vegetable oil and little water and then bring to a simmer. The glaze is done when it is glossy and slightly sticky. Be careful not to burn it as once the sugar caramelises it will turn quickly. Of course, as everything is black anyway you can't tell so you just have to estimate when to stop from the consistency and the aroma.
While the glaze is simmering, heat your oil to around medium heat. The chicken will take around 6-8 minutes to cook so keep the heat moderate so as not to over-brown the crust.
Dredge the chicken in flour and add to the hot oil. The chicken is done when it floats and is a light golden colour, probably around 6 minutes or so if it's quite a thick thigh fillet. Set aside the chicken to rest a few minutes.
To serve, drizzle the chicken with the hot glaze, slice and serve on a plate with plenty of tartare sauce.