Once you have unlocked all the skills, this becomes very easy. I gained this achievement near the beginning of the Eight Diagrams level on Chapter 1, but should be attainable on pretty much any level you have a few weaker enemies.
Be sure to have maxed at least your Kick Attack tree in Basic stance, and the Seal of Levity tree in the Magic Stance. Hold LT and Press X to lay a seal on the ground and cause enemies near you to float in the air. Once this is done, simply press the "X" button multiple times to use your kick attack. I killed the first weak enemy with my second kick of 4, and still had a weak enemy floating in the air from my seal. Pressing "X" the third and fourth time turned my character toward the 2nd floating enemy and they died, popping the achievement.
This achievement is sort of vague, but I assume you need to kill an enemy without your character touching the ground. Using the kick attack you sort of float yourself for up to 4 attacks before landing on the ground. By using Levity Seal (LT + X) and having a few enemies floating, simply spam "X" to kick while in the air until you kill the enemies. This might take a few attempts, but it is the only way I was able to pop this achievement.