Duke Evald is desperate to stop his scheming relatives from seizing control of his family. His solution is a calculated, emotionless contract: a fake marriage with Lydia, the quiet and unassuming third daughter of a count, in exchange for paying off her family’s debts. The Duke believes he has found the perfect, obedient pawn who will cause no trouble. What he does not know is that the meek and mousy Lydia hides a scandalous secret. Under her plain exterior is a wildly popular author of "rose" novels, a genre of romantic fiction about men written for women. Far from being a passive bride, Lydia sees the Duke and all the handsome men surrounding him not as nobles, but as living inspiration for her next story. She begins a secret "rotten observation diary," documenting every interaction, every glance, and every rivalry she witnesses, eagerly imagining the romantic and dramatic scenarios unfolding between the men in the ducal household.

The core conflict arises from this double life. The Duke believes he is orchestrating a convenient partnership, while Lydia believes she is front-row audience to her own private drama. However, her behavior is anything but that of a typical noble lady. She stares too intently, she blushes at the wrong moments, and she frequently gets lost in her fantasies. This very strangeness, which would scandalize high society, instead fascinates the Duke. He becomes increasingly curious about the real woman hidden behind the contract. What began as a purely business arrangement slowly transforms as Evald finds himself experiencing his first genuine feelings, his "first love," for his surprisingly unconventional fake fiancée. The narrative explores whether a relationship built on a lie, with one partner secretly objectifying the other for fictional stories, can become something real.

The story is set in a standard European-style noble court society, complete with lavish balls, strict social hierarchies, and family political struggles. The main characters are Duke Evald, a rational and powerful nobleman who is intelligent but emotionally inexperienced, and Lydia, a seemingly plain wallflower who is secretly a passionate and observant creator. A notable narrative focus is the tension between Lydia’s professional fantasies and her growing personal feelings for the Duke, forcing her to stop seeing him as a character and start seeing him as a partner. Another major arc involves the Duke’s discovery of her secret identity as a novelist, which threatens to destroy the trust between them. The completed manga spans three volumes released between 2021 and 2024.