Lin Wan, a history student, knows the history of the Demon Slayer Corps in the Taisho era by heart. One day, she transmigrates and finds herself a frail girl from a collateral branch of the Ubuyashiki family. Though afflicted with lung disease, she carries a vow to rewrite tragedy and help the Master with her modern knowledge, protecting the young lives destined to fade, especially the Insect Hashira, Shinobu Kocho, whose beauty is as delicate as a butterfly, but whose life is tragically short.
She predicts crises, improves medicines, and refines tactics, trying to turn the tide at key moments in the story. But she never imagined that her very presence would become the greatest variable: Shinobu's curious gaze grows ever more intense, Tanjiro's journey takes a new turn ahead of schedule, and the Upper Rank demons' schemes are quietly rewritten. As the fates recorded in her journal are crossed out one by one, and gentle bonds intertwine with brutal battles, she gradually loses sight of whether she is protecting others or trying to break free of fate alongside Shinobu.
The warm, healing everyday life at the Butterfly Mansion, thrilling battles against demons, and delicate bonds of mutual salvation: amid the storms of the Taisho era, a journey to rewrite fate, sparked by a transmigrator, is slowly unfolding. And the secrets concealed in the shadows of history are gradually coming to light as the story veers from its original course...
