Slice the chicken breasts into long strips and place in a bowl in the fridge.
In a small saucepan, combine sake, mirin, soy sauce and sugar. Simmer until sugar is dissolved. Let cool and pour over the chicken. Let marinate 3 hours. Soak 12 wooden skewers at least 30 minutes to prevent burning.
Thread the chicken on the skewers, folding the meat accordion style. Preheat the grill (or barbecue) and place the skewers on a roasting tray. Grill while frequently basting with the remaining marinade and turning so all sides brown, about 10 minutes.