Ginga Eiyuu Densetsu Gaiden (1999) serves as the second OVA adaptation exploring side stories from the Ginga Eiyuu Densetsu novel series. This installment delves into the pre-Battle of Astarte endeavors of Yang Wen-li from the Free Planets Alliance and further follows the escapades of Reinhard von Müsel and Siegfried Kircheis within the Galactic Empire. Amidst the narrative, Spiral Labyrinth shines a light on Yang's rise to fame following his heroic civilian rescue mission at El Facil. Simultaneously, Reinhard and Kircheis face challenges aboard the Hameln II and later navigate a high-stakes duel regarding a mining dispute. The story unfolds with intrigue as Reinhard embarks on a mission to retrieve a stolen prototype, ultimately culminating in the impactful Third Battle of Tiamat that alters the course of the war in commemoration of Kaiser Friedrich IV's 30-year reign.