Amon, titled the Dragon Emperor, founded and ruled the territory that evolved into Cassandra Prison. To shield his domain from invaders, he constructed an extensive network of deadly defensive traps. These fortifications, however, unintentionally claimed the lives of his own soldiers, including his son Zenos. This loss proved catastrophic, leading his abandoned surviving forces to turn against him.

These events drove Amon into bitter isolation within Cassandra's confines. Detached from reality, he nurtured a delusional conviction that he still commanded a powerful army and governed a flourishing realm, oblivious to the true desolation surrounding him.

When Raoh campaigned to conquer Cassandra, Amon confronted him. During this clash, Amon initially failed to recognize Raoh's elder companion—later revealed as Amon's own brother. Amon unleashed his signature martial art, the Taikyoku Ryuken technique "Hiryuu Genbu," projecting dragon-shaped energy. Raoh deflected the attack with ease, demonstrating superior prowess.

Facing defeat, Amon triggered a mechanism causing violent tremors to crush Raoh and his allies. As the structure collapsed, Amon declared Zenos his successor. Souga, part of Raoh's group, informed Amon that Zenos had perished due to his own traps. Accepting this truth moments before death, Amon was buried under falling debris. Uighur, one of Raoh's followers, then assumed rulership of Cassandra.