"Akuyaku Reijō Tensei Oji-san" centers on a middle-aged office worker who, after passing away, reincarnates into the body of a young noblewoman in a fantasy world. This noblewoman, Tia, is destined to become a villainess in the story of a popular otome game. The protagonist, retaining memories of his past life, must navigate the complexities of this new world while attempting to avoid the tragic fate that awaits Tia.

The narrative explores the protagonist's efforts to alter the predetermined storyline. Using knowledge from the game, the protagonist seeks to change Tia's relationships with key characters, including the game's heroine and the male leads. The story delves into themes of redemption, identity, and the consequences of one's actions, as the protagonist grapples with the moral implications of manipulating events to ensure Tia's survival.

Key characters include Tia, the reincarnated protagonist; the heroine, whose actions drive much of the original game's plot; and the male leads, each with distinct personalities and roles in the story. The interactions between these characters are central to the plot, as the protagonist works to reshape Tia's relationships and avoid the pitfalls that lead to her downfall in the original game.

The series blends elements of comedy, drama, and fantasy, presenting a unique take on the villainess reincarnation genre. The protagonist's perspective as an older man in a young woman's body adds a layer of complexity, influencing decisions and interactions in ways that set the story apart from similar narratives. The plot unfolds through a series of strategic maneuvers, emotional confrontations, and unexpected twists, keeping the audience engaged as Tia's fate hangs in the balance.