Neptune Family

The Neptune Family is the royal bloodline that rules the Ryugu Kingdom of Fishman Island.

Void Century
Princess Poseidon lived during the Void Century and made a pact with Joy Boy. She would use her powers to command the Sea Kings to bring Noah to the surface and activate its intended mission, for which the details would be revealed when raised. However, Joy Boy failed in his commitment to Poseidon due to unknown reasons.

Otohime's Hope
After five years, Queen Otohime managed to get a thousand signatures to promote the co-existence between fishmen and humans. After the Sun Pirates split into three factions, a giant wrecked ship carrying World Nobles arrived at the Fishman Island main entrance and the ship was in need of an emergency entrance. Otohime then rushed to the scene.

She arrived just in time to keep some of the Sun Pirates from killing a World Noble named Mjosgard, who also happened to be their former owner. She saved the noble from a fired bullet, getting grazed in the arm in the process. Some weeks later, Mjosgard was healed and allowed to leave (albeit very ungrateful for their mercy). Otohime decided to go with him much to the shock and disapproval of her subjects and family. She asked them to trust her and humanity, which everyone reluctantly complied with. After one week, she returned to the island having somehow negotiated with the World Nobles and holding a paper said to be "The Hope of Fishman Island".

One day in Gyoncorde Plaza, the box holding all the collected signatures suddenly caught fire. In the ensuing confusion, Otohime was shot. Amidst the chaos, Vander Decken IX marked Shirahoshi with his Mato Mato no Mi powers. Shirahoshi, who was stunned seeing her mother get shot, did not noticed his presence. As she fell to the ground, her sons immediately came to her side. Fukaboshi swore revenge, but Otohime told him not to be angry for her. Otohime reminded her sons about their promise to protect Shirahoshi.

Fishman Island Arc
After the Straw Hats arrived at Fishman Island, Fukaboshi, Ryuboshi, and Manboshi searched for them, wanting to pass on a message from Jinbe. King Neptune later invited Luffy and the Straw Hats to his palace. In the palace, Luffy met Shirahoshi, who explained that she had been staying in Hard-Shell Tower for ten years because Vander Decken IX possesses some kind of "curse". Meanwhile, Neptune heard about Shyarly's prediction and mysterious mermaid kidnappings. The king and the palace guards tried to capture the Straw Hats only to be defeated and tied up. The princes returned to the palace, but they were locked out. Zoro listed his demands and Fukaboshi gave him Jinbe's message. After Luffy took Shirahoshi out of the palace, Hody Jones, Decken, and their crews entered the palace much to the surprise of Neptune.