Gather all ingredients: chilled fruit juice, aged rum, simple syrup, and ice cubes.
Pour the fruit juice into the blender, filling it about halfway to leave room for blending.
Add the aged rum to the blender, which will contribute a rich, spicy aroma and deepen the flavor.
Pour in the simple syrup or sugar syrup to add sweetness and balance the boozy notes.
Top off the mixture with ice cubes, ensuring the blender is at least two-thirds full for proper chilling and texture.
Secure the lid on the blender, then pulse a few times to start breaking up the ice.
Blend on high speed until the mixture becomes smooth, thick, and slushy, with no large ice chunks remaining.
Stop the blender and check the consistency — it should be icy yet scoopable with a velvety texture.
Pour the rum slushie into chilled glasses or cups, allowing the vibrant crimson hue to shine through.
Optionally, garnish with a slice of fruit or a sprig of mint for color and aroma.
Serve immediately with a straw or spoon, and enjoy the refreshing, icy sensation with rich rum flavors.
