The Berserker Armor is a suit of highly durable armor forged by dwarves. Wearers of the armor are aptly named Berserkers.
The Berserker Armor was originally forged by dwarves in the Age of Man, imbued with a violent od purposed for drawing out and manifesting its wearer's negative emotions. The armor eventually finds its way into the hands of the man who would become known as the Skull Knight, used by him for centuries to combat demonkind. However, its malevolent nature grew too much for him to bear, and so he entrusted it to his friend, the witch Flora. In her care, it remained locked away.
It is eventually entrusted to Guts after Flora's spirit tree mansion is invaded by apostles of Griffith's reborn Band of the Hawk. In spite of Grunbeld's immense strength, even after his fire dragon transformation, Guts easily withstands his attacks after donning the Berserker Armor and overwhelms the apostle in their clash.
The armor's ominous od overtakes its user's mind, suppressing their fear and perception of pain. This allows for the transcendence of subconscious limitations placed on the human body, granting its wearer extraordinary gains in strength, endurance, and tenacity. It can temporarily repair several debilitating injuries in the heat of battle: reinforcing broken bones and forcibly reallocating dislocated joints, while piercing flesh with thin barbs and spikes in the process. Such invasive reparation can lead to its wearer's untimely death, however, piercing into and reconstructing their injuries until their last drop of blood. Rather than actually healing its wearer, the armor heals itself when pierced by powerful thrust attacks.
In addition to the perilous nature of the armor, it can induce insanity, or "Berserker rage", by drawing out the wearer's most negative emotions, therefore dissolving the differentiation between friend and foe. It can also cause chronic mental deterioration, providing a hotbed for its user's inner darkness to fester. Upon inducing Berserker rage, the armor's helm takes on the appearance of its wearer's inner beast. In Guts' case, the helmet and bevor are shaped like the Beast of Darkness' head and can function as a mouth, capable of biting enemies. When the armor is active, the helm's eye sockets glow red and Guts' face is completely obstructed; if in control of his sanity, however, the swordsman's face is partially visible and the helm's eye sockets stop emitting their red glow.