This does NOT involve you keeping an enemie in the air. You must make an enemy bounce of other enemies A good way to to this is to go to training mode (found in intermissions of story mode) and use the "Ether Saber 2" Basic skill to hit both enemies up in a corner of the map. The small one will bounce on the big one. Be sure to keep both of them in the air.
Another way is to use "Samurai Edge" Special Skill with "Rune Soul" Optional Skill in the training stage to hit the small enemy into the big one over and over.