After dying from an illness, a woman reincarnates into the world of a popular fantasy novel as Celine, the selfish, overweight villainess duchess and the older sister of the storys heroine. Aware of the original plot, Celine knows she is fated to be executed by the heroic prince for her cruel actions. Determined to avoid this miserable end, she vows to completely reform herself, embarking on a strict regimen of diet and study to change her appearance and personality. However, her earnest efforts to live a quiet, peaceful life produce an unexpected result. Instead of escaping the narrative's conflict, she finds herself the target of intense, all-consuming obsession from the storys true final boss, Prince Wilfred, who was originally meant to be the ultimate antagonist. The prince, who should be cold and ruthless, becomes a doting and dangerously devoted yandere, showering Celine with overwhelming affection that she never anticipated.

The story is set in a noble fantasy realm and centers on Celine Eldred, voiced by Haruka Shiraishi, whose genuine struggle for self-improvement is the driving force of the plot. Her transformation is not just physical but a fundamental change in character, as she shifts from a spoiled noble to a kind-hearted individual. Prince Wilfred Percival, voiced by Takeo Otsuka, is the powerful and obsessive love interest. His yandere nature creates a tense and thrilling dynamic where his love is both terrifying and sincere, leading to a relationship that is uniquely captivating. The narrative includes key arcs where Celine attempts to trigger death flags only to have her plans backfire spectacularly, and a romance arc where she must navigate the prince's increasingly possessive behavior while trying to protect her new life and find happiness.