01 - Rub lime juice around the rim of each serving glass, then dip into coarse salt or sugar if desired. Set aside until ready to fill.
02 - Place watermelon cubes, lime juice, orange juice, and agave syrup in a blender. Process on high speed until completely smooth and no chunks remain.
03 - Pour the blended mixture through a fine-mesh strainer into a pitcher, pressing with a spoon to extract all liquid. Discard the pulp for a silkier texture.
04 - Fill prepared glasses with ice cubes. Pour strained watermelon mixture evenly over ice, dividing between the two glasses.
05 - Add fresh lime wedges and watermelon slices to each glass. Serve immediately while ice-cold for best flavor.