To Make the Sauce
In a pot, combine soy sauce, mirin and sugar and bring to boil. Lower the heat to medium low and simmer for about 4-5 mins or until the quantity is reduced by about ⅓.
To Make Meatballs
In a bowl, combine chicken mince, chicken fat and salt and mix well until the mince turns sticky.
Keeping 1 tbsp of sake and oil aside, add the remaining ingredients and mix well.
While mixing, gradually add the remaining sake to the mince. Stop adding the sake before the mince becomes too soft to form a ball.
In a pot, bring water to boil. Coat a spoon with oil.
With you left hand, take some mince and squeeze them out through the thumb and the index finger. The chicken mince will form into a ball.
Put the mince on the spoon and place it into the pot. Repeat this process for the remaining mince.
Boil the meatballs for 5-7 mins or until cooked through. Remove the meatballs and set aside. You may do this in batches.
To Grill Meatballs
Heat griller in high heat. Oil the rack/grill where you place the meatballs.
With each flat skewer, put through 3 meatballs.
Brush some sauce on the meatballs and cook for 1-2 mins or until slightly charred.
Turn over and cook for another 1-2 mins. Brush some sauce again, cook 5-10 secs on both sides. Serve immediately.