"ACCA: 13-Territory Inspection Department" is a political intrigue and mystery manga set in the fictional kingdom of Dowa, divided into 13 distinct districts, each with its own unique culture and governance. The story centers on Jean Otus, a high-ranking officer in the ACCA organization, a government agency responsible for overseeing and maintaining order across the districts. ACCA's role is crucial in ensuring the stability of the kingdom, which has enjoyed peace for nearly a century.

Jean is the vice-chairman of the inspection department, a branch of ACCA tasked with auditing and monitoring the activities of the other districts. Known for his calm demeanor and sharp observational skills, Jean is respected within the organization but remains an enigmatic figure. His daily life involves traveling to various districts, conducting inspections, and navigating the complex political landscape. However, beneath the surface of his routine duties, rumors of a potential coup begin to circulate, threatening to destabilize the kingdom.

The narrative unfolds as Jean becomes increasingly entangled in the political machinations surrounding the coup. Key figures include Grossular, the head of ACCA, who harbors his own secrets, and Lotta, Jean's younger sister, who provides emotional grounding and insight into his character. Other significant characters include Nino, Jean's childhood friend and a mysterious figure with ties to the royal family, and the various district representatives, each with their own agendas and loyalties.

As the story progresses, Jean's investigations reveal deeper layers of conspiracy, involving the royal family, ACCA's leadership, and the districts themselves. The tension builds as the possibility of a coup becomes more tangible, and Jean must navigate a web of alliances, betrayals, and hidden truths. The manga explores themes of loyalty, power, and the fragility of peace, all while maintaining a steady pace of intrigue and suspense.

The plot is driven by Jean's dual role as both an investigator and a potential key player in the unfolding political drama. His journey is marked by a series of revelations that challenge his understanding of the kingdom's history and his own place within it. The story culminates in a resolution that ties together the various threads of conspiracy, offering a satisfying conclusion to the intricate narrative.