ACCA—a national body of the kingdom of Dowa that provides public services to the citizens of the country—was established as part of the peace settlement between the king of Dowa and the 13 states of the country during a revolt. One hundred years later, Dowa is in a period of unprecedented peace, due in part to the ACCA system. However, rumors of a coup d'état start to surface. Jean Otus, the second-in-command of the inspection department of ACCA, is charged with inspecting all 13 state branches. What will he discover as he performs his audit? Intriguing and mysterious, ACCA: 13-ku Kansatsu-ka is a politically-themed mystery that reveals a world of diverse cultures and lifestyles, with intricate connections between its characters, as the truth of the coup d'état slowly unfolds.

With a cartload of fur pelts in tow, traveling merchant Kraft Lawrence stops by the village of Pasloe. According to local folklore, centuries ago, one of the villagers made a promise with the wolf deity Holo, who swore to bless Pasloe with bountiful harvests of wheat. Yet, as time passed, such stories became little more than relics of the past. After quickly finishing his business in the village, Lawrence sets out to his next destination. His journey, however, takes an unexpected turn when he discovers a nude, animal-eared girl sleeping among his pelts. Even more surprisingly, the youthful-looking woman claims to be Holo—the wolf of legend. Holo wishes to return to her hometown in the north, and though their first encounter is rocky, she convinces Lawrence to accompany her on her travels. In return, she vows to earn her keep, using her quick wits and lifetime of experience to help her newfound companion in his dealings. As they continue their journey, Lawrence and Holo take advantage of whatever economic opportunities they come across, often landing in situations that put both their business skills and their relationship to the test.

Shinichi Chiaki is quickly making a name for himself as the principal conductor of the revitalized Roux-Marlet Orchestra, and Megumi Nodame Noda has made leaps and bounds as a pianist at the Conservatoire de Paris. However, tensions mount between the two as Nodame feels left behind by Chiaki's growing success and his close friendship with legendary piano prodigy Rui Son. Disregarding her teacher Professor Charles Auclair's advice, Nodame enters another piano competition in an attempt to jumpstart her own performance career. Meanwhile, those around Chiaki and Nodame are at their own crossroads. Rui begins to doubt herself after hearing Nodame's playing and being denied tutelage from Auclair; Maestro Franz von Stresemann faces the reality of his mortality; pianists Yunlong Li and Tatiana Vishneva feverishly prepare for a competition, while the latter also struggles with her growing feelings for oboist and fellow student Yasunori Kuroki. As Chiaki, Nodame, and their friends continue on their respective journeys, they must not only strive to stay true to themselves, but also remember where it all started.

Right as he is about to earn a promotion, a salaryman meets an untimely demise. Taking pity, a mysterious being grants him a second life in the land of Galdardia as a teenager. Choosing the name Luciel for himself and a role as a healer, the young man sets off for the nearby town of Merratoni. There, he learns that healers are a coveted resource, yet they often take advantage of others for monetary gain. Vowing to be different from other healers, he joins the local branch of the Healers' Guild and begins unlocking his magical potential. After failing to save someone with his magic, Luciel is determined to get stronger. To improve his physical strength and hone his magic skills, he registers as an adventurer and takes rigorous training under Brod, the chief instructor of the Adventurers' Guild. Soon, Luciel gradually finds his way through Galdardia, gaining a reputation as a selfless healer who aids others regardless of expense.