Elizabeth Thompson, commonly called Liz, is a demon weapon and the older sister of Patricia Thompson. She and her sister were raised on the streets of New York, most specifically the Brooklyn area, where they survived by using their ability to transform into weapons to commit crimes. This earned Liz the nickname the Devil of Brooklyn. Their lives changed when they encountered Death the Kid, who saw them transform into guns and asked them to become his weapons. After agreeing, the sisters moved to Death City and enrolled at the Death Weapon Meister Academy, where Liz was placed in the EAT class. She eventually became a two-star weapon after the collapse of Arachnophobia and later a member of the elite team Spartoi.

Liz has a mature and level-headed personality, often acting as the straight man within her trio. She is the most sensible and grounded of the group, frequently reining in the obsessive-compulsive tendencies of Death the Kid and the childish, manic behavior of her younger sister, Patty. Despite her generally cool-headed demeanor, Liz has a strong fear of ghosts and other paranormal phenomena, which can provoke irrational reactions. She also shows common teenage concerns, such as worrying about makeup and shopping, and is self-conscious about having a smaller chest than her younger sister. Underneath her current responsible exterior, Liz retains a pragmatic and occasionally streetwise edge from her criminal past, but she is deeply devoted to her sister, once stating she cannot imagine life without Patty.

Her primary motivation is to protect and support her sister and her meister, and she is committed to leaving her old life behind. She wants to be a reliable weapon for Kid and a good older sister for Patty, though she can be easily exasperated by their eccentricities. Her role in the story is that of one half of Death the Kid's twin pistols, forming a three-person team that is one of the main protagonist groups. Alongside Kid and Patty, she participates in missions to collect evil souls and combat threats to world order. Over the course of the series, she develops from a thuggish ruffian into a responsible and dependable ally, learning to channel her power for good.

Key relationships include her close bond with her sister Patty, whom she both cares for and tries to keep in line; her partnership with Death the Kid, whom she respects but often has to manage; and her interactions with other DWMA students and faculty. As a demon weapon, Liz can transform into a single pistol or, together with Patty, form a pair of twin pistols for Kid to wield. Through soul resonance with Kid, they can combine into a more powerful cannon-like form. In her human form, she is a capable fighter, and she and her sister can collect the souls of their targets in the magazines of their gun forms. If Kid is absent, Liz can wield Patty in her weapon form and vice versa. She also works part-time as a waitress in the spin-off series Soul Eater Not!.