Dark Knight

At 3rd level, you can withstand the burden of your ebon armor. You gain proficiency with heavy armor and you can still gain the benefits of raging while wearing it.

Your armor helps suppress your feelings until they're ready to be unleashed. While you are wearing heavy armor and you're not raging, you can add your Rage Damage value to ability checks and saving throws against against attempts at discerning your intent, emotions or thoughts.

Soul Eater

Also at 3rd level, you can turn your suffering into strength. When you enter your rage and at the start of each turn you are raging, you can choose take an irreducible 1d6 damage. Until the end of that turn, your weapon attacks deal extra necrotic damage equal to 1d6 + your Constitution modifier.

If you score a critical hit while Soul Eater is active, you gain temporary hit points equal to the necrotic damage dealt.

If you are below half your maximum hit points, you can choose to maximize both the damage you take and the necrotic damage you deal with this feature.

Shadow Wall

At 6th level, you gain resistance to necrotic damage.

Additionally, you can draw harm away from others. When a creature within 15 feet of you takes damage while you are raging, you can use your reaction to take that damage instead.

Dark Mind

At 10th level, your imposing presence aids you in both combat and in conversation. You can interrogate a creature alone for at least 5 minutes. At the end of this time, you can make a contested Charisma (Intimidation) check against its Charisma (Deception) check. If you are successful, you can ask it up to three questions, which it must answer truthfully.

The creature has disadvantage on this check if you have damaged it in the last 24 hours and it either is below half its maximum hit points or if it was knocked unconscious within that time frame.

Once you use this feature, you can't use it again until you finish a short or long rest.

Quietus

At 14th level, you can sacrifice yourself to end your foes. When you hit a creature with a melee weapon while raging, you can expend up to half your hit dice. Roll the expended hit dice and both you and the target take additional necrotic damage equal to the number rolled, ignoring necrotic resistance.

Once you use this feature, you can't use it again until you finish a long rest.

Replica Berserker Armor

Heavy armor, rare (requires attunement by a barbarian)

An emulation of the infamous armor worn by the Black Swordsman. While attuned to this armor, you are proficient with it and can still gain the benefits of raging and Fast Movement while wearing it.

As a reaction when you are reduced to 0 hit points, you can remain conscious and gain temporary hit points equal to twice your barbarian level and if you're not raging, you can enter a rage without expending a usage. These temporary hit points last until your rage ends. If you are at still 0 hit points either when the rage ends or your temporary hit points run out, you fall unconscious. You don't start making death saving throws until you fall unconscious.

Once you use this property, you can't do so again until the next dawn.