Captain Anton Fellner served under Imperial Duke Otto von Braunschweig on Odin during the late Goldenbaum Dynasty. In 796 UC, he participated in arresting Marquis Klopstock after an assassination attempt against Kaiser Friedrich IV, voicing concern over breaching the estate gates due to a statue of Kaiser Rudolf.

When the Lippstadt Rebellion erupted, Fellner backed Duke Braunschweig yet proposed assassinating Reinhard von Lohengramm to prevent prolonged war. After Braunschweig rejected this plan, Fellner independently led a force to kidnap Reinhard's sister, Annerose von Grünewald, intending her as leverage. Reinhard's forces anticipated and thwarted the attempt.

Following this failure, Fellner surrendered to Reinhard, expressing disillusionment with Braunschweig's leadership—"casting pearls before swine." Reinhard accepted his defection, assigning him to chief of staff Paul von Oberstein. Fellner became Oberstein's close aide and advisor, rising to rear admiral.

Serving under Oberstein, Fellner provided strategic counsel and gauged his superior's reactions to political developments within Reinhard's empire. He remained a loyal subordinate through the Imperial Civil War, participating in key events including post-Lippstadt League consolidation and the imperial capital relocation. His Annerose kidnapping operation directly accelerated open hostilities, prompting Braunschweig and fellow nobles to flee Odin.