1/2 cup low-sodium soy sauce
1/2 cup mirin
1/4 cup sugar
3 tablespoons brown rice vinegar (or more if using a less intensely flavored vinegar, such as rice wine vinegar)
1 tablespoon water
2 teaspoons cornstarch
In a small saucepan over medium heat, whisk the soy sauce, mirin, sugar, and vinegar. Bring to a simmer and cook for 2 to 3 minutes, stirring until the sugar is dissolved.
As the glaze simmers, in a small bowl or liquid measuring cup, whisk the water and cornstarch.
Whisk the cornstarch mixture into the glaze and continue to simmer for about 5 minutes, until slightly thickened.
Transfer the glaze to a heat proof jar and let cool completely.
Do Ahead: The glaze can be made 2 weeks ahead. Store in the jar in the refrigerator.