Neptune Family

Rule over the undersea Ryugu Kingdom on Fish-Man Island belongs to this royal line, which King Neptune leads. Fronting its military are the Neptune Brothers, namely Fukaboshi, Ryuboshi, and Manboshi, and the ranks under them draw mostly on the Ammo Knights. The house traces its roots into the Void Century, when Princess Poseidon struck a bargain with Joy Boy, pledging to bend her command of the Sea Kings toward lifting the ship Noah, whose true purpose was to be disclosed only after it surfaced. For reasons left unexplained, Joy Boy never fulfilled his end of that promise.

Neptune took the throne around twenty-six years ago, after the mermaid seer Shyarly foretold his father's death, which duly came to pass. Shyarly further predicted that a princess would be born within a decade. Neptune married Otohime and had four children by her: Fukaboshi, Ryuboshi, Manboshi, and finally Shirahoshi. Otohime devoted herself to closing the rift between fish-men and humans, even sparing the World Noble Mjosgard and escorting him away, and she returned from Mary Geoise clutching a document said to embody Fish-Man Island's hope. Tragedy cut her mission short: a gunshot killed her amid the panic of a fire, at nearly the same moment Vander Decken IX branded the young Shirahoshi with his power.

The house faced its darkest hour when Hody Jones and the New Fish-Man Pirates overran Ryugu Palace, capturing Neptune along with his sons and parading the royals at Gyoncorde Plaza for execution. Breaking in, the Straw Hat Pirates freed the king and princes and turned the battle so the realm could celebrate Hody's defeat. The family later swore to Shirahoshi's friends that they would meet again. With the Levely approaching, they journeyed to Mary Geoise under Garp's escort, where Shirahoshi grew close to Vivi and Rebecca and was menaced twice by the World Noble Charlos before Mjosgard intervened to shield her. During the Egghead broadcast, Neptune and Shirahoshi heard Vegapunk reveal that she ranks among the Ancient Weapons.

King Neptune sits at the head of the house as reigning monarch of the Ryugu Kingdom. His late wife, Queen Otohime, campaigned for peace with humanity before her death. Their sons, the Neptune Brothers Fukaboshi, Ryuboshi, and Manboshi, command the kingdom's army. The youngest child, Princess Shirahoshi, is both the reborn ancient weapon Poseidon and the long-prophesied mermaid princess. At the deepest root of the bloodline stands the original Poseidon, the Void Century princess who first bound her fate to Joy Boy.