Duke Maruki Baumburg (マルキ・バウムブルク) is Princess Kagura's uncle. He desires to obtain Lordship over Cydonia and control of Cydonia's Ethnarch by using Yoko as his pawn. He is the owner of the Sklodowska Mansion.
Despite being Kagura's uncle, Duke Maruki is Kagura's political enemy.
Duke Maruki and Itaru are allies due to shared hatred of Princess Kagura.
Duke Maruki intends to use Yoko as his pawn to obtain control of the region of Cydonia and the Odeon Bach.
Duke Maruki uses an unnamed woman to pose as Yoko's biological mother in order to have her brought to his mansion. He is shown to be cruel to her, hitting her in the face for trying to protect Yoko.
- The Baumburg family is described as a bunke of the Dornburg family. This suggests that Duke Maruki is the younger sibling of whichever parent Kagura Dornburg inherits her royal blood from, and that he established his own family because he was not next in line for the throne.
- Baumburg is a German reading of Kishiro (木城), the surname of the mangaka of GUNNM.
- Maruki (まるき) is a rare Japanese first name. It's not clear whether the katakana is meant to be read as "Maruki", or as "Marquis" instead.