"Sex Demon Queen" is a supernatural fantasy anime that centers on the life of Lilith, a powerful demon queen who rules over the underworld with an iron fist. The narrative begins with Lilith's sudden arrival in the human world after a failed coup in her realm forces her to flee. Stripped of much of her power, she must navigate the complexities of human society while concealing her true identity.

The story intertwines Lilith's efforts to regain her strength and reclaim her throne with her interactions with a group of humans who become entangled in her plight. Among them is Kaito, a college student with a mysterious connection to the supernatural, who inadvertently becomes Lilith's anchor in the human world. As Lilith adapts to her new environment, she forms uneasy alliances with other supernatural beings who have also been exiled or are hiding in the human world. These include Azazel, a fallen angel with a grudge against Lilith, and Seraphina, a rogue demon hunter who initially seeks to destroy her but later becomes a reluctant ally.

The plot thickens as Lilith discovers that her exile was orchestrated by a shadowy faction within her own court, led by her former advisor, Malphas, who seeks to usurp her throne. To regain her power, Lilith must retrieve fragments of her soul, which were scattered across the human world during her escape. Each fragment is guarded by powerful entities, leading to a series of intense battles and strategic confrontations. Along the way, Lilith's character evolves as she grapples with her own morality, the consequences of her past actions, and her growing attachment to the humans who aid her.

Themes of power, loyalty, and redemption are explored as Lilith balances her ruthless demonic nature with the empathy she begins to develop for humanity. The series also delves into the dynamics of trust and betrayal, particularly in her relationships with Kaito and her supernatural allies. The narrative builds toward a climactic showdown in the underworld, where Lilith confronts Malphas and his forces, culminating in a resolution that redefines her role as both a demon queen and a protector of the fragile balance between worlds.

The anime blends action, intrigue, and character-driven drama, offering a layered exploration of its protagonist's journey from a feared ruler to a more nuanced figure striving for redemption and justice.