Whenever you reduce an enemy to 0 Hit Points or score a Critical Hit against an enemy, you can strike terror into nearby foes. When you do so, each creature of your choice in a 30-foot Emanation originating from you must make a Wisdom saving throw against your Maneuver save DC. On a failed save, a creature has the Frightened condition for 1 minute. At the end of each of the Frightened creature's turns, the creature repeats the save, ending the effect on itself on a success.
Once you use this feature, you can't use it again until you finish a Short or Long Rest unless you expend one Battle Die (no action required) to restore your use of it.