Broil or grill the chicken wings until they are charred over about half their surfaces.
In a medium pot, bring the sake and mirin to a boil over high heat. Reduce the heat to medium, add the sugar, and cook until the sugar is dissolved. Stir to prevent burning.
Add the shoyu and chicken wings, and bring the mixture to a boil. Cook over low heat for 30 minutes. At the end of the cooking, the sauce will be thick and glossy.
Strain the sauce through a strainer lined with cotton cloth, discarding the wingtips. The other parts of the wing are quite tasty.
Let the sauce cool to room temperature, then refrigerate for as long as a month. Reheat the tare before using it, and once every week between uses. Or freeze it.
This tare (basic sauce) can be used for more than simply flavoring yakitori (chicken skewers). All summer you can use portions of the sauce to grill: chicken, pork, fish, or just about anything you can cook over charcoal, food you cook on skewers, or not! Add some orange juice, honey, fruit preserves, spices, or other flavorings and voila: teriyaki sauce.