In a fantastical royal court, the narrative follows a young noblewoman known as the villainous daughter, Letitia. The typical storyline of a reincarnated villainess avoiding her doom is subverted when it is revealed that the reincarnated person is not Letitia herself, but her loyal and knowledgeable maid, Rune. Armed with the foresight of an otome game, Rune attempts to guide her mistress away from ruin. The initial crisis strikes during the game's standard "condemnation event," where Letitia is unjustly accused of harassing a rival Saintess candidate, Cecil, leading to her public engagement annulment by her then-fiancé, a second prince. However, Letitia displays a resilience rarely seen in such scenarios, refusing to be humiliated.

Immediately following this downfall, a divine phenomenon occurs. The first prince, Jules, steps forward as Letitia's new protector. A mark known as the Crest of Love or Love Crest (often referred to as a lust crest or lust mark in mature contexts) appears on Letitia, designating her as a true Saintess candidate and identifying Prince Jules as her destined partner. The central conflict arises from the unique mechanics of this fantasy world: the Saintess's dormant power is awakened and amplified through sexual intimacy with her destined partner. Consequently, the more physical their relationship, the more powerful Letitia becomes, transforming her from a discarded noble into an "invincible saintess".

The story navigates several notable narrative arcs, beginning with the "Condemnation and Unexpected Rescue" which establishes the new pairing. This is followed by the "Awakening of the Saintess," where Letitia and Prince Jules must contend with the world's requirement for them to consummate their bond against the backdrop of courtly intrigue. A significant twist is the presence of a second Saintess candidate, Cecil, whose own crest may be fraudulent or illegitimate, establishing a rivalry for the title of the "true" Saintess. Later arcs, such as the "Kidnapping and Jealousy Arc," see Letitia targeted by rivals, which fuels Prince Jules's protectiveness and leads to intimate confrontations. Political threats also emerge, involving a queen who has turned to dark magic.

The primary characters include Letitia, a proud and composed Duke's daughter who adapts quickly to her new circumstances and the presence of a reincarnated maid. Prince Jules is depicted as a devoted and handsome first prince whose role is to satisfy his destined partner's desires while genuinely loving her. The maid Rune serves as the audience's proxy, using her knowledge of the original game's plot to help Letitia, only to find the story has deviated into an "ecchi route" she never anticipated. Opposing them are Cecil, the potentially false Saintess, and antagonists corrupted by dark powers. The setting is a standard European-style fantasy kingdom where strict social hierarchies clash with the absolute priority given to Saintess candidates, regardless of their rank.