In April 793 UC, Reinhard von Müsel and Siegfried Kircheis, while waiting for their next assignment, visits their alma mater in Odin. They are warmly welcomed by the students there, who respect them greatly. After observing the school for a day, Reinhard and Kircheis finally receive their new assignments in the Imperial Military Police. The next day, while browsing through the archives in the Military Police headquarters, Reinhard discovers a case handled by Ulrich Kesler during his tenure as a military police and is impressed by his unorthodox method of protecting ordinary civilians from the oppression of the Military Police. However, when he finds out that Kesler's efforts were ultimately futile, he breaks out into a rant about the degenerate state of the Galactic Empire that is only cut short by new orders from the Chief of Military Police. He and Kircheis are ordered to return to their alma mater to investigate the apparent murder of Karl von Reifeisen, a student who died the night before.
Prequel to the original series, focusing on Reinhard and his steps up the chain of command in the Galactic Empire. Also focusing on the FPA's Yang Wen-li. A chronicle on how he earned the title "The Hero of El Facile" and his handling of assignments he received after the historic event. Spiral Labyrinth also continues with the background of Reinhard and Kircheis where the first Gaiden left off.
