Lilly, a Beastfallen of mouse physiology, serves as a church helper. Her white hair crowns a childlike stature, a consequence of Beastfallen longevity, though she is over twenty years old. Typically barefoot, she often wears a hooded cloak that shadows her gray eyes.

Overwhelming shyness defines her personality, making her avoid crowds and social interaction. Yet, she devotes herself cheerfully and earnestly to assisting the church's priest, demonstrating fierce loyalty that hints at a deep connection to both him and the church's mission, contrasting sharply with her usual reserve.

Her Beastfallen heritage grants Lilly heightened senses of smell and hearing, the ability to mentally commune with and command mice and rats as familiars, and slowed aging. Beyond these innate traits, she possesses exceptional culinary skills, crafting original recipes noted for their quality, and displays surprising proficiency in martial arts and hand-to-hand combat, frequently wielding a knife.

Lilly appears in episodes like "I'm Not Afraid to Die," interacting with main characters visiting her village. Her role rises to prominence during major events, such as the battle preparations in the final episode where her absence becomes a noted concern amid defense efforts against an impending assault. Her actions consistently revolve around supporting the church and aiding the priest.