On her sixteenth birthday, Viscountess Mille-Feuille Forêt Noire, a member of the long-lived dragonkin race, experiences a sudden and shocking awakening. She regains the full memories of her past life as Charlotte, a human woman who was once the beloved fiancée of Vacherin, the powerful Dragon Duke. Her previous life ended in tragedy when she was murdered, leaving her with only the haunting image of the Duke’s furious, grief-stricken face as her final memory. Terrified of repeating history, Mille-Feuille swears a solemn vow to avoid the Dragon Duke at all costs and live a quiet, peaceful life, hiding the secret of her past.

The world she lives in is the kingdom of Eclair, a realm where dragonkin men transform into rampaging dragons once a month. They can only be calmed by a female relative who donates mana, a painful and draining process that often leaves women weak, bedridden, or even comatose. Mille-Feuille, who possesses a latent and immense magical talent she has inadvertently avoided having officially measured, finds herself unable to stay uninvolved. She develops a revolutionary mana depletion cure that helps women recover, and begins secretly distributing this treatment to improve the lives of her fellow dragonkin.

Despite her best efforts to stay away, fate intervenes when the Dragon Duke, Van, appears in public for the first time in a century. Upon seeing him, Mille-Feuille’s past-life memories fully surface, causing her to collapse. Through a series of twists, she ends up appointed as his personal attendant, forced to serve the very man she swore to forget. As she works closely with Van, the line between her current self and her past-life feelings blurs, and she must navigate a new relationship with her former fiancé while trying to uncover the mystery of her own murder. She also contends with court intrigue, a jealous younger sister of the Duke, and the attention of those who have noticed her secret activities.

Following their growing bond and the resolution of the initial threats, Mille-Feuille and the Dragon Duke marry. However, peace remains elusive. For their honeymoon, they travel to the icy Diamant region to develop natural hot springs as a tourist destination, a project born from the newfound free time dragonkin women have thanks to her cure. The trip is soon complicated by the appearance of Fenetra, the Duke’s cousin and a former fiancée candidate who harbors deep resentment. Mille-Feuille must face another assassination attempt, malcontent political ministers, and a villain whose schemes tie directly back to the secrets of her previous life as Charlotte.

Through these challenges, Mille-Feuille works to improve the kingdom, from solving its tourism problems to stabilizing its politics, all while protecting the new life and love she has built. The story concludes with Mille-Feuille announcing her pregnancy and giving birth to a son, finally securing a future far different from the tragic end of her past life.