The new order of ACCA will soon hold its first-anniversary celebration. To ensure every district is prepared for the festival, Jean Otus—acting as a representative for ACCA's inspection department—is called to travel across the Kingdom of Dowa and help with the arrangements. However, he feels that in times of peace, he cannot relate to his subordinate Parrot, who believes that another betrayal against Dowa is near certain. Meanwhile, work leaves Jean no time to dedicate to his little sister Lotta and the unexpected predicament she seems to be hiding from him. Their best friend, Niino, decides to involve himself and looks for a way to support Lotta. Although Jean believes that Dowa is in no immediate danger, he must ease Parrot's suspicions before the festival and wait for Lotta to open up to him on her own. [Written by MAL Rewrite]

ACCA: 13-ku Kansatsu-ka - Regards was adapted into a Japanese live reading and musical production, which was presented on November 8, 2020. The performance featured footage from the OVA.