"Overlord: Shikkoku no Senshi" is a spin-off film set in the expansive universe of the "Overlord" series, which originates from the light novels by Kugane Maruyama. The story centers on Clementine, a former member of the Slane Theocracy's Black Scripture, and her journey after betraying her organization. Clementine, known for her ruthless and chaotic nature, becomes a wandering warrior seeking to test her strength against powerful foes. Her path intersects with a group of adventurers in the Kingdom of Re-Estize, where she encounters a mysterious warrior clad in black armor, later revealed to be Momon, the alter ego of Ainz Ooal Gown, the protagonist of the main series.

The narrative explores Clementine's motivations and her relentless pursuit of power, contrasting her chaotic personality with the disciplined and strategic nature of Momon. As Clementine challenges Momon to a duel, the film delves into themes of strength, loyalty, and the consequences of one's actions. The clash between these two formidable characters serves as the central conflict, highlighting their contrasting ideologies and combat styles. The story also provides additional context to the world-building of the "Overlord" series, offering insights into the political and social dynamics of the Kingdom of Re-Estize and the Slane Theocracy.

The film maintains the dark fantasy tone of the main series, with a focus on character-driven storytelling and intricate world-building. Clementine's backstory and her interactions with other characters add depth to her role as an antagonist, while Momon's presence reinforces his status as a central figure in the overarching narrative. The film serves as a supplementary piece to the main series, enriching the lore and providing a deeper understanding of the motivations and conflicts within the "Overlord" universe.