Lust is a central antagonist in the anime Fullmetal Alchemist: Brotherhood, serving as one of the seven Homunculi created by the primary villain Father. She is the second Homunculus to be brought into existence and the only female among them. Her name is taken from the seven deadly sins, yet her character does not embody lust in a traditional sense; instead, she uses her physical allure and charm as tools to manipulate others, exploiting their desires rather than acting on her own. This approach distinguishes her from the typical portrayal of the sin.

Her background is rooted in her artificial creation by Father as part of his grand plan to reshape the world. As a Homunculus, she is sustained by a Philosopher's Stone, granting her superhuman physical abilities, rapid regeneration from nearly any injury, and immunity to aging, hunger, and fatigue. She does not require sleep or sustenance and possesses strength and speed far beyond any ordinary human. Her signature combat ability is known as the Ultimate Spear, which allows her to elongate and harden her fingers into razor-sharp blades that can pierce through almost any material. This makes her a lethal combatant in close-quarters engagements.

Personality-wise, Lust is highly intelligent, strategic, and calculating. She possesses a deep disdain for humanity, viewing humans as frail, predictable, and foolish. She takes pleasure in manipulating and discarding them for her own purposes, often using disguises and false identities to infiltrate human society and gather information. Despite her cold and ruthless exterior, she displays a unique maternal bond with Gluttony, another Homunculus, acting as his caretaker and guide. This relationship reveals a softer, protective side that is rarely seen in her interactions with others. Her primary motivation is to serve Father and advance his schemes, but she also harbors a subtle ambition to transcend her artificial nature and become human, though this desire is less pronounced in Brotherhood than in the 2003 adaptation.

In the story, Lust plays a pivotal role as an enforcer, infiltrator, and manipulator. She is often tasked with gathering intelligence and coercing alchemists into creating Philosopher's Stones, which are vital to Father's plan. One of her most notable schemes involves posing as a woman named Solaris to seduce Second Lieutenant Jean Havoc, a subordinate of Colonel Roy Mustang, in order to gather intelligence on Mustang's activities. This ruse ultimately fails due to Havoc's professionalism and Mustang's intervention. She is also involved in key conflicts, most notably a climactic battle at the Third Laboratory in Central City. There, she confronts Mustang, Havoc, Lieutenant Riza Hawkeye, and Alphonse Elric. Despite her formidable abilities and regenerative powers, she is eventually defeated by Mustang, who uses his flame alchemy to repeatedly incinerate her until her Philosopher's Stone is depleted, resulting in her permanent death.

Her key relationships include her creator Father, to whom she is utterly loyal, and her fellow Homunculi. Her bond with Gluttony is the most significant, as she treats him with a motherly affection and serves as his moral compass. She also interacts frequently with Envy, with whom she shares a mutual, though often contentious, working relationship. Her encounters with Roy Mustang are particularly notable, as their conflict is both personal and symbolic. Her underestimation of human resilience and her failure to fully grasp the depth of human emotions ultimately lead to her downfall. Through her actions and eventual death, Lust underscores themes of manipulation, the nature of desire, and the contrast between artificial and human existence.