Place the cherries, ice cubes, and sweetener into the blender.
Secure the lid and blend on high speed for 30-45 seconds until the mixture is smooth and icy, with a vibrant red color.
Stop the blender and check the texture; if it's too thick, add a splash of cold water or juice and blend briefly to loosen.
Taste a small spoonful and adjust sweetness if needed by adding more honey or syrup, then blend again briefly.
Pour the slushie into chilled glasses, allowing the icy mixture to mound slightly above the rim.
Serve immediately with a straw or a garnish of fresh cherries for a refreshing summer treat.