Amschel Goldsmith is a central antagonist and one of the most powerful characters in the narrative. He appears as a tall, pale man with slicked-back black hair, a well-groomed mustache and beard, and an aristocratic bearing, typically dressed in a purple suit. His background lies in the 19th century, where he served as a research assistant to the wealthy Joel Goldschmidt. During their studies, they discovered the mummified remains of a monstrous creature along with two egg-like sacs. When Amschel accidentally cut his finger, his blood dripped onto the sacs, causing them to hatch and reveal two infant girls who were later named Saya and Diva, the Chiropteran queens. While Joel raised Saya as his own daughter, Diva was kept locked away as a research subject, with Amschel responsible for bringing her food and tending to her basic needs.

In 1883, Diva escaped and went on a murder spree, but she chose to spare Amschel and transform him into her first and most powerful chevalier by giving him her blood. This event granted him enhanced abilities and a near-immortal lifespan, allowing him to survive for over a century while maintaining a youthful appearance. After Joel Goldschmidt's death, Amschel took control of the research into Chiropterans and eventually became the de facto leader of Diva's five chevaliers, who are referred to as brothers, and the head of the powerful organization Cinq Flèches.

Personality wise, Amschel is defined by a cold, calculating, and profoundly evil nature. He is driven primarily by a twisted scientific curiosity and an obsessive ambition to understand and manipulate Chiropteran evolution. He views Diva not as a queen to be served but as a prized experimental subject, referring to her as his little treasure. He later confesses that his feelings for her are a possessive form of obsession, claiming it as the ultimate form of love. Despite calling the other chevaliers his brothers, he is largely indifferent to their fates, showing no concern when Karl dies and later ordering the execution of Solomon when he betrays them to side with Saya. He is depicted as a master manipulator and a researcher who will go to any length to satisfy his goals, with no redeeming qualities or moments of sympathy provided for him in the story.

His role in the story is that of the primary hidden orchestrator of many of the conflicts. He is responsible for the creation of the Schiff, a group of artificial, half-human, half-Chiropteran soldiers created through horrific experiments in his quest for perfect warriors. He initially attempts to persuade Saya to join their side, even going so far as to kill a Red Shield contact named Liza and impersonate her to get close to Saya and reveal the truth about her own Chiropteran nature. When Saya refuses, he becomes determined to exterminate her. His key relationships are defined by his scientific pursuits; his connection to Diva is one of controller and obsessed scientist, while his relationship with Solomon, his closest blood relative, is that of a master using a favored pawn.

Over the course of the story, Amschel's true nature and goals are gradually revealed. While he initially appears as a loyal servant to Diva, it becomes clear that his loyalty is a ruse and that he is using her for his own ends. His development is less about personal change and more about the escalation of his machinations and the revelation of his secret projects, such as the Schiff. In the final confrontation, his obsession shifts from Diva herself to her newborn daughters, whom he wishes to claim as new subjects for his experiments after Diva is killed.

As Diva's first chevalier, Amschel possesses a range of notable abilities that mark him as exceptionally powerful. He has superhuman strength and speed, enough to easily catch and crush Saya's arm and snap her sword in two. He can communicate telepathically with other chevaliers and exhibits telekinetic powers, able to break objects with a gesture. He is the only chevalier besides Diva to demonstrate the ability to shapeshift, taking on the forms of other people, including Liza and even Diva herself, to deceive his enemies. In his full Chiropteran form, he transforms into a large, demonic, purple creature with six limbs, consisting of two arms, two legs, and two wings, and can unleash a powerful blast of purple energy from his voice. Despite being impaled and struck by lightning, he is able to survive and return in a partially transformed state, showing his immense resilience. He is ultimately defeated when he is stabbed with Saya's blood-covered sword, which causes him to crystallize.