Geigen Huber Grisela, often referred to simply as Hube, is a supporting character in the series and a cousin of Gwendal von Voltaire from his father's side of the family. His background is defined by a significant fall from grace. Prior to the main storyline, Hube was a demon noble whose bigotry and ambition led to numerous deaths, a dark period in his past that remains a source of deep shame. As punishment for these terrible acts, his cousin Gwendal banished him from the Demon Kingdom of Shin Makoku. The banishment came under the guise of a quest to search for a lost artifact known as the Great Demon Flute, or Mateki, forcing Hube to spend twenty years in exile.

During his long exile, Hube's personality underwent a profound transformation. Initially, he was a bigot who harbored strong prejudices against humans and half-breeds. However, his experiences in the human world, particularly meeting a human woman named Nicola, gradually changed his outlook. His past misdeeds, however, left him haunted by guilt and a deep sense that he was undeserving of happiness. Upon being reintroduced into the story, Hube is portrayed as a world-weary and desperate individual, seemingly resigned to his fate. This desperation leads him to serve as the bodyguard for a corrupt lord, but it is ultimately his encounter with the series' protagonist, Yuri Shibuya, that becomes the catalyst for his redemption.

Grisela's primary motivation shifts from a desire to atone for his sins through death to a fierce loyalty and will to protect the one who forgave him. When Yuri discovers the truth about Hube's past, including an incident where Hube unknowingly attempted to kill him, Yuri chooses mercy and begs Gwendal to spare his cousin's life. This act of forgiveness profoundly affects Hube, who then swears absolute loyalty to Yuri. This loyalty becomes his driving force, compelling him to go to extreme lengths to protect the new Maou, even if it means leaving his pregnant partner, Nicola, to fight against a powerful enemy.

His key relationships are central to his character arc. The most significant is with Gwendal, his cousin and the person who exiled him, creating a deep familial rift. Another crucial relationship is with the human Nicola, whom he falls in love with. She is credited with changing his prejudiced views about humanity, and by the time of the main story, she is pregnant with his child, later giving birth to a son named Ernst. He also forms an unexpected bond with the young girl Greta, who sympathizes with his suffering and helps him. Finally, his devotion to Yuri, whom he sees as his savior, defines his actions for the remainder of the series. Even other characters like Conrad, who is initially content to see Hube die because of his past crimes, eventually becomes part of the intricate web of forgiveness and judgment surrounding him.

Hube's development is a classic redemption arc, moving from a position of villainous prejudice and disgrace to one of a humbled, loyal, and loving individual. The outward symbol of his dangerous past is the loss of his left eye, an injury he sustained in an encounter with one of the Four Forbidden Boxes. In terms of abilities, he is a highly skilled swordsman. His prowess in combat is such that he wandered the land seeking a worthy opponent who could end his life, indicating his confidence in his own fighting abilities. Later, his talent is put to use in the service of protecting Yuri and the Kingdom of Shin Makoku.