Sugar is a basic element of teriyaki.
In my opinion and experience, it's best used as a finishing glaze than anything else because of the sugar and how easily sugar burns.
1 cup soy sauce
1/2 cup rice wine--mirin preferred as it's a sweet rice wine
3/4 cup sugar
1 clove garlic, crushed
1 slice ginger, crushed
Combine all ingredients in a non-reactive pan on the stove. Over medium heat, bring to a boil, stirring frequently but watch closely so it doesn't boil over from the sugar. Simmer 5-10 minutes until it's nice and syrupy.
Brush on the meat (or grilled vegies) in the final few minutes of cooking so it sets up as a glaze.