Scythe Master, also known as Helmut von Giuseppe, holds doctorates in psychology and neurology. He serves the criminal organization Inferno, specializing in interrogation, brainwashing, and mental conditioning. He forges and controls elite assassins called "Phantoms" using these techniques.

He developed the first-generation Phantom, Ein, subjecting her to memory erasure and psychological manipulation to create a highly efficient killer. He later applied the same process to a Japanese teenager who witnessed an assassination, erasing his memories to designate him the second-generation Phantom, Zwei. His methods include drug-induced amnesia, hypnotherapy, and intense conditioning to ensure absolute obedience.

He views his subjects solely as instruments, comparing them to firearms. This perspective manifests in a ritual where he applies lotion to Ein's naked body, treating her as a weapon requiring maintenance. His approach varies; while Ein and Zwei undergo memory erasure, the third assassin Drei retains her memories as part of a "thought experiment" testing whether leveraging existing trauma ensures loyalty as effectively as amnesia.

He maintains direct oversight of Ein and Zwei's training and missions, emphasizing their expendable nature. His influence extends beyond physical control, instilling psychological dependency that hinders autonomous function.

In the anime adaptation, Ein assassinates him during Inferno's internal power struggles. Alternative outcomes exist: the original visual novel includes routes where he survives Ein's betrayal and later seeks revenge against Inferno. The OVA adaptation significantly reduces his role, limiting his involvement to Zwei's early indoctrination.

His legacy persists through the Zahlen Schwestern, assassins he engineered. In one game ending, Zwei uses Scythe Master's own conditioning methods to turn these assassins against Inferno, resulting in the extermination of the organization's leadership.