For this achievement you need to have 6 vortexes going at once. You create a vortex by creating a circular shape with your character's trail.
For this, kill every enemy but one (bonus if it moves slowly) and then draw circles like crazy. When you are spamming circles like this it seems to have trouble keeping up, but if you keep spamming it should eventually create enough vortexes for the achievement. Took me about 30 seconds to get this.
Achievement will pop when you've met the requirements.