Dr. Easter operates as a freelance 09 Case Officer in Mardock City, an investigator pursuing justice using experimental technology, often outside standard law enforcement. A brilliant cyberneticist and former Paradise facility researcher, he developed forbidden technologies during the Commonwealth-Continent War, including the polymorphic intelligence Œufcoque and the life-preserving Mardock Scramble 09 ordinance. His motivations shifted from scientific curiosity to a humanistic focus on aiding victims after leaving Paradise.

He rescues Rune Balot from near-fatal injuries, initiating her transformation into a cyborg under Regulation 09 by replacing her damaged skin with Lightite metal fibers, granting her technopathic abilities and enhanced perception. This act establishes him as both her creator and legal protector, assigning Œufcoque as her partner and guardian. Eccentric in behavior, he frequently dresses unconventionally, described as a "punk rocker cosplaying as a physician," though he adopts a refined appearance for undercover work.

His partnership with Œufcoque involves constant bickering and mutual reliance, forming a vitriolic yet deeply trusting bond. With Rune, he displays patience and empathy, gradually viewing her as a surrogate for his estranged daughter due to their similar age and trauma. He actively monitors her psychological state, expressing concern when her dependence on Œufcoque mirrors past unhealthy relationships, and intervenes when she nearly fatally abuses Œufcoque's powers during violent confrontations.

Primarily a non-combatant, he takes direct action in crises, such as arming himself to confront the assassin Boiled when Rune and Œufcoque face danger. His work involves navigating tensions surrounding the ethics of his technologies, particularly reviving witnesses and constraining sentient creations like Œufcoque. He employs advanced systems for investigations, utilizing sophisticated displays in his vehicle for data analysis and mission coordination.