Lily Heineman captains the third unit of Dorothea, a peacekeeping agency under the Unified Zesskia Empire's Ministry of Fairies. She leads her unit in investigating and combating illegal fairy usage and related crimes across the postwar continent of Eastald. Despite lacking the fairy organs that allow others to wield fairies as weapons, she is a capable leader trusted by her subordinates. This positions her as a non-fairy soldier who relies on conventional leadership and tactical skills within an organization frequently engaged in combat against rogue fairy users.

Physically, she is a young woman with light to dark brown hair, typically styled in a high ponytail, and blue eyes. She consistently wears the standard Dorothea uniform appropriate to her role. Specifics regarding her age, birthplace, or pre-Dorothea history are unavailable.

Her duties involve participating in routine Dorothea operations and unit functions, such as conducting shooting drills at the Rodancia quarters and attending social events like Serge Tova's welcoming party for Marlya Noel. While not central to the primary plotlines involving Marlya Noel, Free Underbar, or the Black Fairy Tome, she maintains a steadfast presence within Dorothea's activities. Her role expands during the later stages of heightened conflict involving the Eins Order and the consolidation of the Black Fairy Tome, where she demonstrates her capabilities against escalating threats to the empire.

Her characterization remains focused on her professional role as a reliable unit commander within Dorothea's structure. Information about her involvement in extended media beyond the main series, specific character relationships, internal motivations, or personal development arcs is not provided.