Eiji Sagimiya is a central figure in the world of E's Otherwise, serving as the chief of the psychic research team for the powerful Ashurum Corporation and the commander of its elite special forces unit known as AESES. He is a man whose true motives remain largely obscured, acting with a calm and collected demeanor that masks a deeply calculating and manipulative nature. His physical appearance is that of an adult male with blue eyes and short blue hair, and he is often seen wearing a professional ensemble of a suit, tie, coat, and sunglasses, reflecting his authoritative position within the corporate hierarchy.

Eiji is responsible for bringing the young psychic Kai Kudou and his chronically ill sister, Hikaru, into the Ashurum organization. On the surface, he presents the arrangement as a form of protection and opportunity, where gifted individuals known as E's can be trained to use their powers for the greater good by apprehending rogue psychics. He is fully trusted by the leadership of Ashurum and is a contemporary of another executive, Kazumi, indicating his high standing within the corporation.

Beneath this professional facade, however, Eiji is driven by a deeply personal and enigmatic agenda. He displays an unusual and intense attachment to both Kai and, more significantly, his sister Hikaru. This fascination suggests that his interest in the siblings goes far beyond their value as recruits. It is implied that Hikaru possesses extraordinarily powerful psychic abilities, and Eiji appears to have designs on using her powers to execute a specific plan in the city of Gald, though the full scope of his scheme remains hidden.

The mystery surrounding Eiji is compounded by his own unnatural origin. He is revealed to be an artificially created psychic, brought into existence by his father, and possesses the remarkable ability to resurrect the dead. This background explains his cold, detached perspective and his relentless pursuit of his objectives, as he is a product of manipulation and extraordinary power himself. Over the course of the story, his leadership of the AESES team shatters the naive belief of young recruits like Kai that Ashurum is a purely benevolent force, exposing the corporation and its commander as entities willing to sacrifice others for their own hidden ends.