In a pot, mix soy sauce, mirin sauce, water, sugar, and 6 pcs scallion leaves. Boil for 20 minutes, or until 1/2 cup of the mixture is left.
Slice the scallion for about 2-inch pieces, then cut chicken breast into 1-inch cubes.
Fold each slice of chicken, then insert the stick into the chicken in 45 degrees angle, and press down on the skewer to pierce through the center. Alternate chicken slice with a piece of scallion.
Do the same procedure with the remaining ingredients.
Transfer it all into a baking dish, then brush with sauce mixture each meat.
Preheat oven to 200 degrees F.
Occasionally, brush the chicken meat with sauce mixture and make sure to cook it evenly.
After 20 minutes, transfer your yakitori onto a plate.
Serve with your choice of sauce and enjoy!