In the 2003 anime adaptation of Fullmetal Alchemist, the character known as Sloth operates under the alias Juliet Douglas while serving as a homunculus created through the failed human transmutation performed by Edward and Alphonse Elric. Their attempt to resurrect their mother, Trisha Elric, resulted not in a successful rebirth but in the formation of a shapeless, living mass. This being was discovered by the ancient alchemist Dante, who nourished it with red stones, allowing it to develop into a fully formed homunculus bearing the exact appearance of Trisha Elric. As a homunculus, she possesses the Ouroboros tattoo on the upper left part of her chest and represents the sin of sloth, though her personality reflects the apathy and emotional indifference associated with the sin rather than physical laziness.

Unlike many of her fellow homunculi, Sloth rarely displays intense emotions or takes pleasure in violence. She maintains a consistently calm, composed, and sometimes melancholic demeanor, carrying herself with a quiet, paternalistic manner when interacting with others. This emotional detachment, however, masks a deep internal conflict. She is tormented by persistent, fragmentary memories of Trisha Elric's life, including visions of her sons and her late husband, which intrude upon her consciousness as if they were her own. These memories become a source of profound despair, motivating her primary personal goal. She seeks to kill Edward and Alphonse not out of malice but as a way to sever these unwanted connections to her predecessor and prove to herself that she is an entirely separate being from the mother the Elric brothers lost.

Within the military structure, Sloth adopts the identity of Juliet Douglas, a soldier whose records show conflicting information suggesting she died years before the Ishvalan civil war yet remains on active duty. She serves as the secretary to Führer King Bradley, who is himself the homunculus Pride, allowing her to operate from the heart of Amestris's government and relay information to her master, Dante. In this capacity, she is responsible for conveying orders to other homunculi and overseeing their missions. She gives the order for Lust and Envy to eliminate Maes Hughes after he begins investigating her suspicious background, directly leading to the investigation that puts the Elric brothers and Winry Rockbell on her trail. Her position as a trusted operative is further demonstrated when she assists Envy in recruiting the homunculus Wrath, hiding the young homunculus within her own fluid body to escape pursuit.

Sloth's unique ability as a homunculus allows her to liquefy her body into a pure, watery substance. This power serves multiple functions. She can slip through small openings for infiltration, travel swiftly through bodies of water, and attack by drowning victims or using her liquefied arms as powerful whips or tentacles. When in her fluid state, physical attacks have little effect on her, as she can simply reform from dispersed droplets, as demonstrated when a chemical attack temporarily breaks her apart. She can also absorb surrounding water to regenerate or increase her mass. However, this power has a defensive limitation, as constant, rapid attacks can force her to remain in her fluid state and prevent her from counterattacking effectively.

Throughout the story, Sloth's personal torment grows as she interacts with the Elric brothers. When Edward discovers her true identity as the result of his failed transmutation, he is horrified by her uncanny resemblance to their mother. Sloth uses this resemblance to manipulate them psychologically, acting in ways that mimic Trisha's mannerisms to unsettle her creators. Despite her stated desire to kill them, she develops complex feelings toward the boys and transfers her maternal impulses onto Wrath, whom she treats as a replacement child. Dante dismisses this bond, reminding Sloth that homunculi cannot truly have mothers or sons. In a significant confrontation, Sloth immobilizes Hohenheim, the Elric brothers' absent father, allowing Dante to banish him to the other side of the Gate.

Her character arc concludes with a moment of unexpected development. In her final moments, she appears to accept the memories that had tormented her for so long, exhibiting a trace of maternal affection and offering words that resemble a mother's advice or blessing to the Elric brothers. Edward ultimately defeats her by transmuting her fluid body into ethanol, which causes her to evaporate. Her death, which brings her a form of peace, allows her to escape the painful existence of being a failed copy created from grief and longing.