This is very unlikely going to happen through normal progression of the game. You will need more than 5 enemies around in order to get this achievement, because you will usually an enemy or two as you're building your combo meter. The absolute best area to get this in is extremely late in the game in Arkela Castle - Hall, and only after backtracking. So when you get to this area, continue on until you are done with the Grand Staircase area. Make an extra save just in case. Now you may travel back to that area where there are 6 enemies standing stationary. Bring the Majin into the hallway with the save point, and have him wait there. Now run over and grab the attention of the enemies, and bring them to the hallway. If they don't lunge at you, they'll stay there and not be able to get in the hallway. Now go behind the Majin and command him to do a Lightning Attack. Run in and you should easily be able to get this achievement, specifically if your Friendship level is high. If not, you will get it while raising your maximum levels. See "Brave One" achievement description for more info.