In a small saucepan, combine 1/3 cup water with 1/3 cup agave syrup. Bring to a boil, stir until combined, and let simmer for 3 minutes. Remove from heat and transfer to a pitcher.
Juice the 4 lemons and transfer juice to the pitcher. Add the extra 3 cups of water to dilute the lemonade. Pour in the prepared hibiscus tea and garnish with lemon slices, blueberries, and mint leaves.
Serve over ice at your next cookout or picnic adventure.