Cut chicken thighs into bite-sized pieces (keep skin on). Place pieces into a strainer and give a quick rinse under cold water. Then set it aside for a few minutes and let it drip-off the excess water. Afterwards, place into a mixing bowl.
Add the following ingredients into the mixing bowl: Soy Sauce (2 Tablespoons), Salt (3-4 shakes), Sugar (1 teaspoon), Mirim (1 Tablespoon), Black pepper (few shakes), Ginger Powder (3-4 shakes or 1/2 teaspoon of freshly grated ginger). Give a thorough mix.
Place plastic wrap over the bowl and place in the refrigerator for 1 hour.
After 1 hour, take it out of the refrigerator. Crack in one egg into the bowl. Then use a pair of chopsticks and gently stir-it into the mixture.
Take out a plastic bag (or ziploc bag). Pick-out each chicken piece from the bowl and place into the bag. (Don't dump it in - we don't want all the liquid).
Next, add enough potato starch to cover the chicken. Close the bag and give it a good shake. Flip the bag upside down and shake it as well to get all the sides evenly coated. (Add more starch powder if needed.)
Put oil into a frying pan or pot. Place on medium-high heat and bring the oil up to 180C (350F). Now, gently place each chicken in and cook until dark-golden brown.
Optional: You can pick-out the chicken when they're about 80% done. Raise the temperature of the oil and place back-into the oil for a double-fry. It leads to an even crispier skin.
Serve with rice and enjoy!