Divide the mint leaves and lime wedges between two tall glasses. Muddle with the end of a wooden spoon to release the juice from the limes and the oils from the mint leaves.
Add 8 raspberries and 2 teaspoons agave nectar or honey to each glass, and muddle again to combine.
Full the glasses with ice, pour 1 ½ ounces of rum into each glass. Fill to the top with soda water.