Path of the Kakodaimon
Barbarians of the Path of the Kakodaimon have often made a pledge with an infernal being, similar to a warlock. They are granted great power at the cost of their souls, and their patrons rarely let them forget, marking them as accursed with reddish skin colours, great horns, and forked tongues.
Devil's Deal
Starting at 3rd level, you've forged a pact with a powerful devil. While raging, you have resistance to fire damage, and you can use a bonus action to mark a creature within 60ft of you. A marked target takes an additional 1d6 damage from your weapon attacks.
Gargantuous Rage
Starting at 6th level, your infernal blood has infused its power into you, granting the power of size and might. When you enter you rage, you can choose to also become enlarged, as if by the enlarge spell. While enlarged by this feature, you can choose to have your weapon attacks deal fire damage, instead of their normal damage type.
You can use this feature an amount of times equal to your Constitution modifier, regaining all uses at the end of a long rest.
Soulbound Presence
Starting at 10th level, your devilish power has infused itself more, granting you the power of presence and fear. You have advantage on Deception and Intimidation checks against humanoids, and can use Strength instead of Charisma for Deception and Intimidation checks.
Being of Carnage
Starting at 14th level, your infernal power has fully infused into you, strengthening your might and presence. You can add your rage bonus to your Strength or Charisma ability checks, and your carrying capacity doubles.