"Bakumatsu Gijinden Roman" is set during the Bakumatsu period in Japan, a time of political upheaval and transition from the Tokugawa shogunate to the Meiji Restoration. The story centers on Roman, a self-proclaimed "phantom thief" who operates under the alias Nezumi Kozo. Roman is a charismatic and skilled thief who steals from corrupt officials and wealthy elites, redistributing the wealth to the poor and oppressed. His actions are driven by a personal code of justice, blending Robin Hood-like altruism with a flair for theatrics.

The narrative unfolds as Roman navigates the complexities of a society in turmoil. He is pursued by the shogunate's forces, including the determined and resourceful inspector Shinsaku Takasugi, who views Roman as a criminal undermining the fragile order of the era. Despite their adversarial relationship, both characters share a mutual respect, and their interactions highlight the moral ambiguities of the time. Roman's exploits also attract the attention of Oryo, a skilled swordswoman and former assassin, who becomes both an ally and a rival. Her involvement adds depth to the story, as her motivations and past intertwine with Roman's mission.

The series incorporates historical elements, blending real-life figures and events with fictionalized drama. The backdrop of the Bakumatsu period provides a rich setting, exploring themes of loyalty, justice, and the clash between tradition and modernization. Roman's heists are often elaborate and symbolic, targeting those who exploit the weak while challenging the status quo. The narrative balances action, humor, and moments of introspection, offering a multifaceted portrayal of its characters and their struggles.

As the story progresses, Roman's actions begin to influence the broader political landscape, drawing him deeper into the conflicts of the era. His encounters with various factions, including pro-shogunate loyalists and anti-government rebels, reveal the complexities of his role as a thief and a symbol of resistance. The series concludes with a reflection on the transient nature of power and the enduring impact of individual actions during times of societal change. Through its engaging plot and well-developed characters, "Bakumatsu Gijinden Roman" presents a compelling exploration of justice and morality in a turbulent historical period.