A plain and stubborn fallen noble lady named Letitia is growing anxious as she reaches marriageable age without any suitable suitors. Her childhood friend, Ethelbert, is a prince of extraordinary beauty and notorious for being a playboy who constantly changes his romantic partners. He frequently teases Letitia about her lack of romantic experience, much to her annoyance, yet she secretly finds herself drawn to him, though she believes a relationship between them is impossible.

The story follows Letitia as she decides to pursue a practical, loveless marriage with a man who seems a perfect match for her serious personality. Ethelbert strongly objects to this engagement, but Letitia ignores his warnings. Her fiancé suddenly elopes with another woman, breaking off the engagement. Unbeknownst to Letitia, Ethelbert was secretly behind the scheme to sabotage her wedding. He then reveals his true feelings and proposes to her, a confession she accepts. However, soon after, Ethelbert collapses. Letitia is told to kiss him to save his life, and the overwhelming pleasure of that act unlocks his secret he is an incubus who survives on spiritual energy, and his true form includes mysterious appendages called Nyoro that he has kept hidden.

The narrative unfolds in a fantasy noble setting centered on a royal court. Letitia is a practical, uptight woman who prioritizes logic over passion, while Ethelbert is a charming and cunning prince whose playboy reputation is a facade for his deep-seated loneliness and his hidden nature as an incubus. Key supporting characters include Ethelbert's younger brother Richard and various fairies and magical beings that populate this world.

Several notable narrative arcs drive the story. The initial arc focuses on the push and pull between Letitia and Ethelbert, with her failed engagement and his subsequent confession leading to their marriage. The wedding night arc introduces the Nyoro, which Ethelbert has been hiding, and Letitia must come to terms with this unexpected aspect of his incubus nature. A later arc involves an incident at a tea party where Ethelbert uses his Nyoro to playfully tease Letitia under her skirt, testing her ability to maintain her composure in public. The story also features an arc where a changeling a human swapped for a fairy child appears, leading to Ethelbert being falsely accused of being a fairy. He is imprisoned and isolated, unable to receive energy from Letitia, weakening him severely. Letitia must then find a way to prove his innocence and save him from this dangerous situation. Another arc introduces a magical ring given by a leprechaun that amplifies pleasure, which Ethelbert uses to discipline Letitia, causing her to gain more allure and catch the unwanted attention of another man.