In the popular web novel Brigitte Wants to be Happy!, Princess Yerenika of Livovny is a side character doomed to a tragic end. But when a woman is reincarnated into the story as Yerenika, she resolves to change her terrible fate and escape death. Unexpectedly, she has joined the narrative at an earlier point in time—both the main characters and the villain have yet to be born!

Yerenika successfully derails the story from its intended course by preventing the abduction of her sister Theresia by Euredian, the king of Bellecourt—a plot point that would have set a series of tragic events in motion. However, Yerenika's plan goes awry when Euredian kidnaps her instead and takes her to his nation. Given that the air of Bellecourt is thick with magic and toxic to Yerenika's weak body, she resorts to her final strategy.

Originally, Euredian went on to marry Lady Soleia Elodia and father Dekalb, the villain of the web novel who led an entire slew of characters to their deaths. Now, Yerenika must rewrite history and prevent Dekalb from ever existing—by seducing his father and making Euredian marry her instead!