Nyx's existence began in tragedy during a catastrophic maritime disaster. A violent storm slammed into his family's ship, sending it to the depths. Confronted by drowning in his youth, Nyx desperately pleaded for survival, offering anything in exchange for life. This cry summoned Erebos, a demonic entity embodying darkness itself. Erebos saved Nyx through possession but allowed his parents to drown, cursing him with a painful immortality that trapped him in an ageless state for over two centuries. The experience forged a profound fear and hatred of the sea within him, its sounds forever echoing the trauma of Erebos's possession.

As Erebos's immortal host, Nyx became the conduit unleashing Thanatos—life-draining monsters—into Arcadia. Consumed by the desire to end this curse and find peace through death, he dedicated centuries to seeking the "Queen's Egg," a prophesied purifier capable of confronting Erebos. He founded the Aube Hunters, an organization of Purifiers dedicated to combating Thanatos, recruiting members including Rayne, J.D., and Hyuga. Discovering Angelique, a schoolgirl with latent purification abilities, led him to invite her to join the Aube Hunters at Sunlit Mansion, though she initially declined to pursue medical studies.

Nyx projected an aura of elegance and mystery, often addressing Angelique as "mademoiselle." He cultivated refined habits like playing the piano and tending flowers, though his attempts at gardening consistently failed, a poignant symbol of his curse. Despite inner turmoil, he masked his pain with projected kindness and grace to support others. He wielded a whip against the Thanatos and served as the Aube Hunters' strategic leader.

In *Second Age*, Erebos's influence surged, resulting in full possession. Nyx oscillated between his own consciousness and the entity's control, sometimes acting against his allies. He voiced deep self-loathing for drawing Angelique into his fate, acknowledging that Erebos's actions through him had destroyed her home and family. Under moonlight during a confrontation, he explicitly implored Angelique to end his life, believing it the only way to sever Erebos's hold on Arcadia. His internal struggle climaxed in a direct battle against Erebos during the final conflict. Following the entity's defeat, Nyx vanished, his ultimate fate unresolved yet implying release from his immortal burden.