Vander Decken IX, a fish-man bound by a centuries-old vendetta, traces his lineage to the pirate captain Vander Decken, who once sought to obliterate Fish-Man Island with the colossal ark Noah. Though the initial plot failed, the Decken family nurtured an enduring hatred toward the island’s royals. As the ninth heir, Vander Decken IX embraced this legacy, consumed by obsessive loathing for King Neptune and his bloodline. Raised within Fish-Man Island’s aristocracy under House Decken, he cultivated profound resentment toward the royal family’s perceived complacency in combating anti-fish-man discrimination. His fixation crystallized in childhood upon encountering Princess Shirahoshi, whom he vowed to marry. When threats against her provoked his exile, rejection twisted his obsession into vengeance, fueling a decade-long campaign of assassination attempts. Empowered by the Mato Mato no Mi Devil Fruit, which allows marked targets to be struck with unerringly thrown projectiles, he launched relentless long-range assaults on Shirahoshi, even propelling Noah itself toward her sanctuary. This vendetta briefly intertwined with extremist Hody Jones’s uprising against the monarchy, merging personal spite with broader insurrection. His pallid, angular features, jagged teeth, and gaunt physique contrasted with opulent attire echoing noble roots. Demeanor shifted from cold precision to feverish mania when invoking Shirahoshi or the royal family, his every action dictated by the Decken creed: destroy the Neptunian line, whatever the cost. Defeat at the Straw Hat Pirates’ hands halted his reign of vengeance, thwarting Noah’s catastrophic descent through communal intervention. Imprisonment silenced his schemes, leaving no trace in later records. The Decken legacy endures as a grim testament to hatred’s generational poison, its echoes a reminder of how ancient grudges perpetuate cycles of violence within Fish-Man Island’s fractured society.