Retzel works as a waitress at Café Kuronekotei among other automata. She possesses ash gray hair in twin ponytails and red velvet eyes. Her attire typically includes a purplish-brown beret, a black cape over a white and gold-trimmed outfit, light gray stockings, and black shoes. She carries herself with grace and propriety, though she sometimes makes blunt or cruel remarks. As the sole automata of foreign origin on staff, she often feels lonely.

Originally crafted in Lobelia by the Imperial Army for observational research, her design specialized in infiltration and subversion. This made her systems resistant to standard memory resets, allowing her to retain combat protocols and loyalty to her homeland even after joining Kuronekotei. Her skills include proficiency with knives and firearms; she initially hid these abilities by stealing kitchen utensils and concealing weapons in a suitcase.

Retzel's core struggle involves adapting to postwar life. She secretly attempted to contact Lobelia for new orders, only to discover the war had ended and her faction dissolved. Believing herself obsolete and purposeless, she chose self-annihilation by requesting military disposal. Haizakura intervened, convincing her of alternative purposes for existence. The military performed another memory reset, though traces of her past identity persisted.

Following this event, she remained at Kuronekotei. She formed a bond with a stray black cat, symbolizing her gradual acceptance of peace. Her interactions with Haizakura include physical closeness, such as hugging and approaching her on a bed during nighttime conversations. These experiences contribute to her ongoing journey to redefine her role beyond wartime functions.