Luis Hartman is a young boy who lives in the city of Blumstadt. He is the son of Vincent Hartman, a well-known private detective. After losing his mother to an illness, Luis lived with his father, whom he greatly admired. He enjoyed reading adventure comics such as Wolf-Man Comics, a pastime that reflected his youthful imagination, though he remained firmly grounded in rational thinking.

Luis’s life is shattered when his father is murdered while investigating a series of killings attributed to a so-called “Grave-Digging Vampire.” The crime scene shows signs of immense force used to extract blood from the victims, leading the police and the public to suspect a supernatural culprit. Luis, however, stubbornly insists that the supernatural does not exist and that the killer must be a human being. Driven by grief and a desire for justice, he takes up his father’s deerstalker hat and vows to solve the case himself. He spends months conducting his own investigation, refusing to accept any explanation that involves vampires or magic.

Luis is initially skeptical and even hostile when he encounters the Arne Detective Agency, a group of young detectives led by the vampire Arne Neuntöte. He is surprised that Arne, who appears even younger than himself, claims to be a detective. Despite his reluctance, Luis eventually shares information with Arne and his assistant Lynn Reinweiß. He provides a crucial clue: his father was clutching a handkerchief embroidered with flowers, which Luis realizes his father had used blood from his own wound to turn the petals red. This deduction helps the group identify the real killer, a café owner named Adelina.

Luis’s motivation remains focused on avenging his father and proving that the murderer is human. His determination leads him to confront Adelina alone, discovering that she is actually a witch who has been using an earth golem to squeeze the victims to death and water white flowers with their blood to turn the petals red. In the confrontation, the golem stabs Luis, fatally wounding him. Arne intervenes by drinking a vial of blood and transforming into his powerful adult vampire form, but Luis is beyond saving. In his final moments, Luis is forced to accept that the supernatural is real.

After his death, Arne’s associate Amy, a necromancer, reanimates Luis’s body. As a reanimated corpse, Luis retains his consciousness and a single purpose: to take revenge. He uses a sword to stab Adelina, killing her and finally avenging his father. Once his revenge is complete, he returns to eternal sleep and is buried in the family cemetery alongside his parents.

Luis Hartman is characterized by his strong-willed, rational nature, his deep love for his father, and his refusal to believe in the supernatural until it is literally forced upon him. He is brave enough to investigate on his own, intelligent enough to piece together clues, and emotionally driven enough to risk his life for justice. His role in the story serves as the catalyst for the first major case of the series. His key relationship is with his father, whose memory guides him, and his interactions with Arne and Lynn force him to confront his worldview. His development is a tragic arc from denial to acceptance, followed by a brief resurrection for closure. He has no supernatural abilities of his own; his notable abilities are his keen observation and deductive skills, inherited from his father.