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Sonja is shown to have a caring personality as the overseer of the medical division. Her kind actions brings a lot of respect and concern from the rest of the division. However, she is also seen to be stubborn as well as loyal to her friends, as seen when she decides to help Stocke escape from Alistel after hearing about Hugo's conspiracy, and when she attempts to snap Rosch out of his depression in Celestia.
Sonja has feelings for Rosch, and shows great concern when he and/or Stocke goes out on dangerous missions. Depending on the player's actions, Sonja will marry Rosch and become pregnant.
She is also shown to have a frightening side when it comes to thaumatechnology, especially when it somes to Rosch's arm.
Sonja used to have a brother that was a thaumatech engineer. He performed surgery on Rosch, since he was particularly fond of him, he made him his gauntlet. He dies two years before the start of the game. It was considered an honorable death, that he was considerate of his men to the end. Rosch supported her through his death.
- Kiel appears to have a crush on her.
- A common speculation among fans is that Sonja was originally supposed to be a party member, due to her being depicted holding a staff and wearing a breastplate, despite the absence of combat in her line of work. In addition, she was portrayed with a shield in a preliminary version of the box art (which only depicts party members), but she was omitted in the final version of the cover. It is possible that the developers decided that her role of healer was too singular, and demoted her to an NPC whilst transferring her skills over to Marco or other characters.