It suppresses the sensation of pain and fear, allowing the wearer to exert 100% of their physical potential.
The armor does not technically grant new powers; instead, it removes the user's subconscious physical limiters.
The armor is described as a "villainous item" because it eventually consumes its wearer. Berserker Armor | The Evil Wiki | Fandom
Instead of healing, the armor brutally "fixes" injuries by injecting thin metal spikes into the wearer's flesh to pin broken bones and joints back together, allowing them to continue fighting until their body completely fails.
The armor's appearance shifts to reflect the wearer's "inner beast." For Guts, the helmet takes the form of the Beast of Darkness , a manifestation of his trauma and bloodlust. The Terrible Price