Add cherries, sweetener, ice, and water (or cherry juice) into the blender.
Secure the lid and blend on high speed for about 30-45 seconds, until the mixture is smooth and icy in texture.
Stop the blender and check the consistency; add more ice if you desire a thicker, more slushy texture, then blend briefly to incorporate.
Pour the cherry slushie into chilled glasses, allowing the vibrant red mixture to flow smoothly over the rim.
Serve immediately with a straw or a spoon, enjoying the cool, bursting flavor of fresh cherries.