In medium saucepan, combine mirin, sake, sugar, ginger, garlic, and soy sauce. Bring to boil over high heat and cook until sugar has dissolved and sauce has thickened slightly, about 8 minutes. Remove from heat and let cool completely.


Put chicken in a large bowl, pour marinade over and turn to coat. Chill 1-3 hours.


Prepare grill. Thread chicken onto wooden skewers. Transfer marinade to a small saucepan and boil over high heat until it has the consistency of barbecue sauce, about 15 minutes.


Grill skewers, basting with thickened marinade and turning frequently to prevent scorching, until chicken is caramelized and no longer pink in center. (about 6 minutes). Serve with remaining sauce on side.