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.
After five years, a giant wrecked ship carrying a World Noble arrived at the Fish-Man Island's main entrance and the ship was in need of an emergency entrance. Otohime then rushed to the scene. The ship was owned by Donquixote Mjosgard, who traveled to Fish-Man Island to retrieve his slaves, who were by that point the former members of the Sun Pirates. Otohime arrived just in time to save 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 Fish-Man 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.
Fish-Man Island Saga
Fish-Man Island Arc
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. Hody and his crew then invaded the palace and captured Neptune in the ensuing conflict.
Meanwhile, Luffy and Shirahoshi were confronted by Decken at Coral Hill, where the princess rejected Decken's proposal. After defeating Decken, Luffy took Shirahoshi to the Sea Forest, where they met Jinbe.
Hody later brought Neptune to Gyoncorde Plaza, where he planned to execute him. The princes arrived and confronted the officers of Hody's crew only to be defeated and captured as well. After seemingly falling for a trap, Shirahoshi, Jinbe, and Megalo were also taken to the plaza. Right after Luffy saved Neptune from execution, the Straw Hats quickly freed the king and the princes and Hoe took them to safety. The princes later returned to fight Hody. Once the New Fish-Man Pirates were defeated, the royal family celebrated the victory. The moment the Straw Hat Pirates left, they made to Shirahoshi the promise to meet again.
Four Emperors Saga
As the time for Levely approached, Shirahoshi was asked to accompany her father and brothers. Shirahoshi initially refused, saying that she was too scared and not wanting to break her promise to Luffy. Fukaboshi told her that she should come for their mother's sake.
As the news of Luffy's exploits at Totto Land spread across the world, Neptune read about it on the newspaper and learned that Jinbe joined Luffy's crew. Given Jinbe's actions against Big Mom, Neptune planned to declare Fish-Man Island under the Straw Hats' protection. As Shirahoshi decided to accompany her family, they were ready to depart for the Levely.
Later, they arrived at the Red Port, where they made acquaintances with Monkey D. Garp as he escorted them to the bondola. Along the way, Neptune interrupted a quarrel between Garp and Sterry. Neptune and Garp then parted at the bondola, and as he and his family rode it to Mary Geoise, Neptune was happy that Shirahoshi marveled at the sun and sky.
At the socializing plaza, several royals tried to get Shirahoshi's attention and she was overwhelmed as she accidentally offended them. She then befriended Vivi and Rebecca after hearing them talk about Luffy, even though Ryuboshi tried not to associate his sister with a pirate. Meanwhile, Fukaboshi conversed with Viola.
Later, Charlos tried to take Shirahoshi by force. Before Neptune did anything drastic, Mjosgard intervened on Shirahoshi's behalf and knocked out Charlos with a spiked club before ordering for Shirahoshi to be set free. After Charlos was taken away, Mansherry healed Shirahoshi's bruises, and Neptune acknowledged that there are good humans and that Mjosgard's actions had saved Otohime's dream. Neptune later went to the conference room with the other kings and queens to begin the Levely.
Wano Country Arc