Heat peanut butter and 3/8 cup water in a nonstick saucepan over low heat.
Add maple syrup, coconut milk, garlic, soy sauce, fish sauce, 3/8 cup water, and red pepper flakes to peanut butter mixture, stirring well after each addition.
Bring peanut mixture to a boil, stirring constantly. Reduce heat to low and simmer, stirring, until flavors blend, 5 minutes.
Remove from heat, cover, and let rest to blend flavors, 10 minutes.