"Rail Romanesque" is set in a world where autonomous trains, known as Raillords, operate independently across the land. These Raillords are anthropomorphized as young girls, each embodying the spirit and characteristics of their respective trains. The story centers on Mizuki Touko, a young woman who inherits her grandfather's railway company, Hinomoto Railway, after his passing. The company is on the brink of collapse due to financial difficulties and competition from larger corporations. Mizuki, determined to revive the company, discovers a hidden Raillord named Aira, who had been dormant for years. Aira, along with other Raillords, becomes instrumental in Mizuki's efforts to save Hinomoto Railway.

The narrative unfolds as Mizuki works to restore the company's reputation and infrastructure, facing challenges such as outdated technology, rival companies, and the need to modernize while preserving the legacy of traditional railways. The Raillords, each with distinct personalities and abilities, assist Mizuki in various tasks, from improving train services to competing in races that showcase their capabilities. The series explores themes of perseverance, innovation, and the importance of preserving cultural heritage in the face of modernization.

Key characters include Aira, the cheerful and determined Raillord who becomes Mizuki's closest ally; Iyo, a reserved and knowledgeable Raillord with a deep connection to Hinomoto Railway's history; and Kiko, a spirited and competitive Raillord who often challenges Aira. Other Raillords and human characters contribute to the story, each playing a role in the revitalization of the railway company. The interactions between Mizuki and the Raillords highlight the bond between humans and machines, emphasizing collaboration and mutual respect.

The plot progresses through a series of episodic challenges, with Mizuki and the Raillords tackling issues such as route optimization, customer satisfaction, and technological upgrades. The series balances lighthearted moments with more serious undertones, addressing the economic and social pressures faced by small businesses in a rapidly changing world. By the end of the series, Mizuki's efforts begin to bear fruit, showcasing the potential for traditional railways to coexist with modern advancements. "Rail Romanesque" presents a unique blend of slice-of-life storytelling and railway-themed adventure, appealing to fans of both genres.