Mix th e soy sauce, sake, ginger root and garlic, and marinate chicken in misture for 1 hour. Drain chicken, reserving the soy mixture. Heat oil in skillet until hot. Cook chicken until done, about 15 minutes. Heat water, sugar, and soy mixture in 3 qt sauce pan. Boil and stir for 2 minutes. Stiir in the green onions. Place chicken on rice and spoon sauce over top.