Preheat grill. Combine sugar, soy sauce, sake, garlic, scallions, ginger and sesame oil in a medium size flat dish. Add the steak and coat well with the marinade. Let marinate at room temperature for 30 minutes, turning once. Remove meat from marinade and grill on each side for 2 to 3 minutes, for medium-rare. Remove from grill, cover and let rest for 5 minutes. Slice thinly against the grain.