In a small saucepan, combine all ingredients, except water and cornstarch, and heat over medium heat. Stir vigorously until the sugar dissolves and the Teriyaki Sauce is evenly combined.
Pour the water and cornstarch into a small bowl and stir to combine. This prevents cornstarch lumps from forming. Add 3 tablespoons of Teriyaki Sauce to the cornstarch mixture. Mix well.
Combine the ingredients in the bowl, then add them to the saucepan, whisk, and heat until the sauce thickens.
Be aware that the sauce can simmer very quickly, so be ready to reduce the heat at any time. Depending on the size of the saucepan you're using, it might take from 5-10 minutes. When the sauce reaches the right thickness, set it aside to cool.
Pour it into a bottle or an airtight container once cooled and serve it with grilled or fried vegetables and meat. You will never taste anything like them!