In a small saucepan over medium heat, combine the sugar, vinegar, soy sauce, and garlic. Bring to a boil. Watch very carefully until the sauce thickens, stirring occasionally, about 6 to 8 minutes. Add water as needed, a tablespoon at a time, to dilute slightly.
Recipe by Between Carpools at https://betweencarpools.com/basics-a-sushi-dinner-isnt-complete-without-sweet-sauce/