Your rages is as bottomless as the abyss. Maybe that is why deep and dark powers lurking within the abyss starts flowing through you. Shadow rises and gather around living creatures whenever you rage, and these shadows can even manifest as your own weapons. You made this darkness your own as it makes your heart its own home.
A barbarian who accepts the abyss and allows it to dwell within their soul becomes an agent for darkness, however, such abyss empowered rage is not something anybody else could control or manipulate. Being an abyss agent doesn't change barbarian's morality, but it does grant them dark powers even some warlock's may envy.

Raging Abyss

At 3rd level you learn a new way to use your rage.
As a bonus action you can consume a single use of your rage to spawn pools of shadow underneath all creatures within 30 yards you can see. These pools last for 1 minute.
Whenever you attack an enemy standing within one of these pools, then you gain +3 to your attack rolls.
Whenever an enemy attempts to leave one of these pools, then you can use your reaction to perform 1 weapon attack against them regardless of your distance from that enemy. This attack counts as an opportunity attack.

Rage of the Night

At 6th level you learn how to summon an abyssal copy of yourself.
As an action you can summon an abyssal copy of yourself within one of your abyssal pools created with Raging Abyss feature (a clone can only be summoned in an occupied location). Only one copy of you can be summoned at one time and these copies can not leave your abyssal pools. Upon leaving your abyssal pool - the copy will be instantly banished back into the abyss.

The abyssal clone has the same stats, hit points, abilities and gear as yours. Its turn will follow directly after yours. You can freely move your clone (no action required). If you did not use your action to attack during your turn, then you can can command your clone to use its action to attack. Otherwise, it will take dodge action on its turn.

Your abyssal clone never requires your command to use its reaction, such as when making an opportunity attack.

Army of the Abyss

At 10th level your Rage of the Night feature becomes even more powerful.
Instead of summoning 1 clone, it will now summon up to 2 clones (each clone can only be summoned in an occupied location). And whenever you active your Rage, then all of your clones will gain benefits of Rage as well.

In addition, while you are standing in one of your abyssal pool created by Raging Abyss feature, you will be immune to magical darkness and gain Blindsight of 120 feet.

Bottomless Abyss

At 14th level your soul becomes consumed by creatures dwelling within the deepest corners of the abyss.
Choose Intelligence, Wisdom or Charisma. Increase your maximum Rage uses by the modifier of the chosen stat. In addition:
* Your abyssal pools created via Raging Abyss feature now will have an effect identical to Sickening Radiance applied at their locations;
* Your abyssal clones summoned via Rage of the Night feature now will have an effect identical to Magic Weapon applied to them.

These effect do not require your concentration and your chosen stat will be your spellcasting ability for these effects.