The late mangaka of Berserk, Kentaro Miura, undoubtedly introduced the Berserker armor as another means to explain how Guts could possibly survive against such powerful demons and gods — filled with rage and the desire for vengeance as he is, he's still human — but it also had a far deeper meaning within the story.
The Berserker armor essentially allows the wearer to push themselves past what's physically possible. For as long as the armor is worn, the user can feel no pain and continue fighting
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