Path of Fury

For some barbarians, a blind anger serves them less well than a focused river of fury. the Path of Fury is one of unbridled emotion; anger and spite focused against a specific goal. When the fury of battle takes over, little can stop you from achieving your goals, and sometimes you might lose yourself to the emotion.

Focused Fury

Starting when you choose this path at 3rd level, you can direct your anger at a specific opponent. If you do so, select an enemy that has dealt damage to you or one of your allies; they become your Focused opponent. You add your proficiency bonus to all attack and damage rolls made against that opponent, and you have disadvantage on attack rolls against any other enemy.

If you take damage while Focusing, you must make a constitution saving throw of 15 or lose your focus. If you take damage from an enemy when raging but not Focusing, you can spend a reaction to Focus on them. Your Focus automatically ends when you kill your chosen opponent.

You can do this a number of times equal to your constitution modifier per short rest. 

Unstoppable force

When you use your Focused Fury ability, your movement speed doubles when moving in a straight line towards your chosen opponent, and you deal an extra 1d6 force damage if you move ten or more feet towards them before your strike. This increases to 2d6 at 9th level, and 3d6 at 15th level.

Momentum

Beginning at 10th level, your very presence in a battle is unsettling to those weak of mind. When you are in a Focused rage, all attack rolls against you not dealt by your chosen opponent are made with disadvantage. Once a creature has hit you, they lose their disadvantage at the end of the round, and for the rest of combat.

Wave of Hatred

Starting at 14th level, if you land the killing blow against your Focused opponent, you can immediately  use your reaction to Focus on another enemy, and make one melee attack roll against them.