The Sixth Battle of Iserlohn begins. The Alliance forces proceeds with Willem Holland's plan of using the main fleet as a diversion to keep the attention of the Imperial forces and allow Holland's squadron to close in to Iserlohn Fortress and breach its walls with a missile bombardment. Holland's plan works initially; however, he is intercepted by Reinhard von Müsel, who has anticipated this move. Reinhard then continues to make full use of the narrow geography of the Iserlohn Corridor and wreak havoc on the Alliance main fleet with his squadron. Gregor von Mückenberger orders the remaining Imperial fleets to engage with the Alliance main fleet as well, which turns the battle into an outright mêlée as the Alliance commander Lasalle Lobos, taking the advice of Yang Wen-li, commits his reserves into the battlefield as well. Within this chaos, the Rosen Ritter succeeds in luring out Hermann von Luneberg, who makes a forced boarding attempt on the Rosen Ritter's strike ship Cheiron 3. Walter von Schönkopf engages with Luneberg on a one-on-one combat and manages to kill him. Meanwhile, while his squadron is being resupplied in Iserlohn Fortress, Reinhard, along with Siegfried Kircheis, is approached by Ulrich Kesler, who reveals to them the truth of the circumstances behind the death of Elizabeth von Luneberg's former fiancé as well as the aftermath of her realising the truth. He then offers Reinhard a book compiled by Admiral Grimmelshausen which records all of the unsavoury deeds of contemporary high nobles, and conveys to Reinhard Grimmelshausen's message that he hopes the book would be of use to him in his ascendancy. However, Reinhard, while grateful to Grimmelshausen, decides to decline his offer as he plans to bring down the high nobles fair and square without resorting to blackmail.
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.
