Place soy sauce , sugar , ginger and pepper flakes in 2 quart sauce pan. Bring to simmer and make sure all sugar is dissolved. Lower heat and add blueberries. Simmer for 10 minutes and bring up to slow boil. Mix cornstarch and water to make slurry. Add to sauce while stirring. Should thicken up instantly. Ready to use hot or could refrigerate to use later. Reccomend using at room temperature after initial preperation. Good in refrigerator for 2 weeks.