Add 3/4 cup water, rice vinegar, sugar, salt, and chili crisp to a small saucepan.
Bring the mixture to a low simmer over medium heat, stirring until the sugar dissolves.
Let the mixture simmer gently for 5 minutes.
In a small bowl, whisk 3 tablespoons of cool water with the cornstarch until smooth.
Slowly pour the cornstarch slurry into the sauce while stirring constantly.
Immediately remove the saucepan from the heat once the slurry is incorporated.
Allow the sauce to cool. It will thicken as it cools. Use right away or refrigerate in an airtight container.