Manstoll appears exclusively in the film *BEM: BECOME HUMAN*. He is a former colleague of Bem from an unspecified earlier time, implying a shared history preceding the film's events. This relationship deteriorates completely, leaving Manstoll consumed by malice and corruption. He emerges as the primary antagonist and architect of the central conflict. Manstoll schemes to manipulate Bem, who lives under the identity "Belm" with a fabricated family within a controlled environment simulating human life. Manstoll's goals center on power and domination, using the pharmaceutical company Doracho Chemicals as a front. His methods include kidnapping Sonia Summers to use her as leverage against Bem. During the climax, Manstoll mutates into a monstrous form. He kills Sonia by impaling her through the heart, an act which triggers Bem's catastrophic mutation and unleashes his full power. Despite achieving this powerful form, Manstoll is decisively defeated by the mutated Bem, who overwhelms and destroys him. Manstoll's corruption and actions serve as a narrative device exploring themes of corruption, the consequences of abandoning principles, and the cost of embracing evil, directly catalyzing Bem's final sacrifice to save Sonia.