Astarte is a homunculus originally created to serve the alchemist Rudolf Eustach. After her master's defeat, she received a three-year probation sentence and was placed under the guardianship of Natsuki Minamiya, serving as her maid.

She has blue hair and blue eyes. Her initial garment was a simple white cloth, which was later replaced by a maid uniform upon entering Natsuki's service. As a homunculus, her face remains largely blank and unreadable, typically devoid of emotional expression.

Her personality is marked by an almost complete absence of emotional expressiveness and a limited, robotic manner of speech; she often replies with a dull-toned "Accept." Gradually, through her interactions while under Natsuki's guardianship, she begins to exhibit more emotion and shows signs of developing her own independent thoughts.

Astarte has no biological parents or relatives, having been brought into existence as a created being. She is recognized as the first successful homunculus implanted with a familiar—a achievement once deemed impossible. Her early life consisted of undergoing various experiments within Rudolf Eustach's secret laboratory.

She possesses a unique familiar named Rhododactylos. It first appeared as two massive arms attached to her back, capable of draining magical energy from other familiars to augment its own power and grant Astarte supernatural strength. In a later form, it manifested as a white humanoid entity, with Astarte herself encased within a green orb in its chest. This form provides immense durability and allows her to employ divine vibrations that can nullify magic.

She participated in several major events, including those concerning the Right Arm of the Saint, the Emissary of the Warlord, the Blazing Angel, the Labyrinth of the Blue Witch, the Banquet of the Observers, and the Return of the Alchemist.