The Separator
Lars: What do you do with a bunch of kids who don't know how to do anything but bang their heads all day long?
Eddie: eyes tearing up You start a revolution, Lars.
— Eddie Riggs before the Battle of Lionwhyte Mines
The Separator is the greataxe used by the legendary Bardbarian, Eddie Riggs, to decapitate his sworn foe Doviculus. The Separator starts as a +1 greataxe, but gains a stacking +1 bonus to attack and damage rolls anytime the wielder kills an enemy. You can have a maximum bonus of +5, and every turn you don't kill an enemy, at the end of your turn, you lose one stack.
Additionally, once you get to +5, you can choose to use your action to spend all charges to call upon the Gods of Metal for inspiration. All enemies within a 15 foot radius of you must make a DC 16 Constitution saving throw or be frightened and all allies within that range get advantage on all attack rolls until the start of your next turn.