In ACCA: 13-ku Kansatsu-ka, the kingdom of Dowa is held together by ACCA, the national body created after a revolt and a peace settlement between the king of Dowa and the 13 states. A century later, that arrangement has produced an age of rare stability, and the country's citizens rely on the system to keep daily life running smoothly. But as rumors of a coup d'état begin to spread, the calm surface of the kingdom starts to crack.
Jean Otus, the second-in-command of ACCA's inspection department, is sent to inspect all 13 state branches and report on what he finds. His travels take him from one state to the next, where he encounters distinct cultures, lifestyles, and political interests that reveal how varied Dowa really is. Each branch adds another piece to the larger picture, and Jean's routine audit slowly turns into a carefully layered political mystery. As he moves through a web of subtle connections among the kingdom's characters, the rumored coup draws closer to the truth, and the balance that has kept Dowa together begins to look far more fragile than it first seemed.