Schierke

Schierke was raised in a forest by the witch Flora and taught to speak with the spirits in fire, water, earth and wind. She is a child, blunt about it, and openly unimpressed by the swordsman she ends up travelling with. Her magic runs on trance: she sits, leaves her body, and directs elementals from a place where a sword is no use to anyone.

That makes her the first ally who can do something Guts cannot. Berserk spends a long time on one man solving every problem by hitting it, and Schierke's arrival changes the shape of the fights. She also becomes the person responsible for pulling him back when the Berserker Armour has taken more of him than it should, which is heavy work for someone that young.

Her name comes from a real place. Schierke is a village in the Harz mountains of Germany, on the road up to the Brocken, the peak where witches were said to gather on Walpurgis Night. Goethe set a scene of Faust there. Miura borrowed several names and most of the magical vocabulary in that arc from the same northern European folklore.