Theresia is introduced as the Count's daughter, much to Puck's shock, as the elf is given to her as a gift. She appears stiff and stoic around her father, and recoils when he attempts to touch her. Despite Puck's fear of her, she quickly assures him she won't harm him and that she knows what it's like to live in a cage, before opening up to him about her life. Describing the change her father went through seven years ago, she states that her mother was killed by a band of heretics, inspiring the demonic change in her father and his appalling bloodlust.
Soon, Puck has to leave in order to help Guts, but assures her that he will come back. However, before Puck can fulfill this promise, Theresia leaves her room on her own, inspired by Puck's own freedom, and walks in on Guts' battle with her monstrous father in Apostle form. Terrified and with her worst fears confirmed, Theresia runs away, but is taken hostage by Guts, who uses the opening presented to blast the Count's face apart and cleave off his head. Theresia cries while Guts torments her father viciously, though it is unknown if she feels he is going too far or is simply overwhelmed by the events.
