Demon fused

Unlike most barbarians coming from homes where they learned to save there strength for raging through, your strength comes from a demon fusing with you. tending to give you a new form that fuses a weapon to your body by using some sort of switch, such as removing your hand like a blade from a sheath or pulling a cord like activating  a chainsaw. this does give you strength outside of this form however you are stronger in this form, gaining healing from blood,  stronger weapons, and near immortality. However this fusion does make it near impossible for you to gain emotional attachment as well as an uncanny nonchalant feeling about death, even when its someone close to you. You can still feel these things but its rarely as strong as that of a normal persons. 

Weapon fused rage.

choose one weapon. whenever you rage you use a trigger to summon it that relates to your weapon such as a pull-cord in your chest for a chainsaw, removing your hand like a sheathe for a katana, or pulling a hilt out of your chest for a greatsword,  it comes out of your head and arms(the end of the weapon at your elbow, extruding from your hand), as your head changes shape to become closer to the demon that fused to you. Your wielding 2 of whatever weapons you chose. you can not change this weapon. the weapon acts the same as whatever weapon it was but gains one dice for damage rolls (for example a longsword would go from 1d8 to 2d8 damage) you have proficiency with the weapon regardless of if you normally do. At level 10 gain 2 extra dice instead of 1 for the damage roll.

Blood fueled

Whenever you kill an enemy roll a d6, heal that much hp. This increases to a d8 at level 6, a d10 at level 10 and a d12 at level 14

Never trust what they tell you.

once you hit level 6 During your rage you may use a reaction to attack someone who has attacked you, whether they hit or not. they must be in the range of your weapon to use this. 

Strength by fear.

during combat whenever you kill an enemy gain 1d6 dice on all attacks. this stacks up to 5d6 damage. once you hit level 14 the cap goes to 8d6. If you surprise an enemy before combat gain 1d6 at the start. 

Demon hearted.

You have learned how to use your demon to near the best of your ability. Your damage from your weapon is sustained even when not raging, while raging gain an extra attack and +2 AC. You may also choose to use both your bonus action and action to do an all-out attack, gaining advantage on your attack, as well as an extra 1d10 damage on it. You may do this a number of times equal to your proficiency bonus.