Spa Island Arc

This ninth filler arc unfolds after the Thriller Bark events and follows the crew's holiday at the man-made Spa Island. It reunites them with the comical Foxy Pirates, last seen during the Long Ring Long Land period.

The plot revolves around two young sisters, Lina and Sayo, and the notebook left behind by their gem-researching father, which the resort's scheming owner is determined to seize.

While the crew enjoys the resort's pools and spas, they meet Lina, her shape-shifting sea raccoon, and her guarded sister Sayo, who clutches a mysterious notebook. Before the sisters can slip away, Foxy and his loyal companions Porche and Hamburg ambush them with a mirror-covered mecha that scatters the slowing Noro Noro Beam everywhere. Foxy snatches the notebook, but Franky and Brook arrive fresh from the baths, and Luffy launches the trio into the sea.

Sayo explains that the sisters are daughters of a ridiculed scientist who believed he could create a genuine gem. He vanished on an expedition and was presumed dead, sending home only his notes and a plea for them to finish his work. The crew is moved by the tale, but the resort owner Doran, who secretly hired Foxy, kidnaps Sayo through a trapdoor. Luffy proposes simply destroying the island to find her faster, and the crew wrecks the place.

Doran corners them by threatening Sayo with a cannon, demanding the notebook. When Sayo reveals their father stayed away only to keep the pursuing Foxy Pirates from endangering them, Lina refuses to surrender it. Luffy uses Gear 3 to split the island in half, and after the dust settles the group discovers an underwater volcano whose rising steam is the final ingredient for the rainbow gem. Realizing the treasure was the gem itself, Doran flees with Foxy's crew in pursuit.

Days later, the sea raccoon delivers a letter to the Straw Hats. The sisters succeeded in crafting the rainbow gem, their father returned alive in time to witness it, and the family now lives happily together. As thanks, the girls send the finished gem to the crew, who admire it just as a sudden shower of candy rains down and the jewel is knocked loose on deck.

The arc holds a few distinctions in filler history, being the first to feature Brook among the crew and the second island Luffy personally destroys after Clockwork Island. It also extrapolates two manga-canon elements, the sea raccoon and the circular rainbow, from a montage of the crew's post-Thriller Bark travels.