Combine the mango cubes, brown sugar, and water in a saucepan and heat gently over medium-low heat, stirring occasionally, just until the mango softens and releases aroma; do not boil aggressively or reduce heavily. Remove from heat, add the lime zest and chili flakes (Use standard crushed red pepper flakes, not powder.), cover, and let steep for about 10 minutes, then strain through a fine-mesh sieve without pressing the solids and allow the syrup to cool completely.
Pour the cooled mango syrup into a large pitcher, add the fresh lime juice and the fine sea salt, and stir until fully combined, then add the ice-cold water and mix gently until the drink is uniform and balanced. Taste and adjust only with more water if needed — sweetness and acidity should already be aligned.
Refrigerate for 1–2 hours until fully cold and integrated.
Fill glasses with ice, pour over the mango lime drink, and garnish with fresh mango slices and lime slices.
