The Giant Mechanical Soldier of Karakuri Castle

Helmed by Konosuke Uda from a script by Atsutoshi Umezawa, this ninety-four minute feature reached screens in 2006 and takes place shortly before the Water 7 storyline. Its closing song is Sayaendo. The picture holds a special place as the first outing to show Gear 2 in motion, and its plot doubles as the in-story account of how Luffy stumbled into the technique. It is also the franchise's second mechanical-island movie and the second time an island proves to be an enormous living animal.

Combing a storm-battered wreck for loot, the crew brings up a lone chest and finds an elderly stowaway named Roba huddled inside. She dangles the promise of a legendary Golden Crown if they carry her home, and Luffy agrees over his crewmates' suspicions. Reaching the destination demands a Turtle Pose, a little turtle that forever points toward the island. As the ship draws near Mecha Island, an arrow-firing robotic defense springs to life, and Roba's son Ratchet glides down to pluck his mother off the deck. His officer General Maji looses the robots and a huge fan, but Zoro turns aside every arrow while Robin snaps Maji's back with her Clutch, and the wrecked Going Merry can no longer sail.

Grounded, the crew picks apart a local folk tune, the Yurari Uta, that Robin had jotted down. Its mentions of a white snake and two moons steer them to a snake-headed rock, and Robin works out that the word for moon can also read as strike. Understanding that the verse points them to strike the serpent's pair of eyes, Luffy shatters the first, and once he cracks the second, an entrance yawns open. Ratchet, pursuing the same prize, throws a party and feigns cooperation. Down in the caverns the crew empties a lake by knocking over an ibis statue, reads the song's closing lines, and finds the ground fossilized and shell-encrusted. When Nami zaps a lance with her Clima-Tact, the whole landmass rouses and shows its real form as a colossal turtle, the same creature that had been calling out to Chopper.

Casting off his disguise, Ratchet announces he will ride the turtle to rule the world and fires up his gigantic mechanical castle to command it. The Straw Hats scatter to fight his henchmen across roller-coaster rails and battle suits while the turtle, which surfaces once every thousand years to lay eggs, drifts toward an inhabited island. Cornered by Ratchet's finest robot, Luffy inadvertently kicks Gear 2 into gear and demolishes it. The crew then merges their strength into Gomu Gomu no Kaiten Ono to crack the castle apart and release the turtle, which lays its eggs undisturbed. Luffy realizes the Golden Crown meant the gold of the hatched shells, though the fragment they grab slides into the water, and Ratchet ends up scolded by his mother.

Preview trailers contained footage absent from the completed movie, among them a two-legged dinosaur robot and daytime versions of the henchmen fights, all dropped for scheduling reasons. Chopper's regular voice actress sat this production out while on maternity leave. What gives the film enduring weight is its handling of Gear 2, since it stages the technique's very first appearance and lays out the doping surge that pumps extra blood through Luffy's body for a short burst of power.