Pluton

Three Ancient Weapons exist, and this battleship is one of them, sharing that rank with Poseidon and Uranus. Its reputation for causing mass destruction earned it the grim label of World's Worst Battleship, and rumor claims a lone volley can wipe out an entire island. Long ago, over the span of the Void Century, shipwrights in the Grand Line city of Water 7 assembled the craft, though today it lies buried far below Mt. Fuji in Wano Country.

Crocodile first raised the subject when he interrogated King Cobra over where the weapon could be found. Later, during the Water 7 Saga, the surviving blueprints for the vessel became the trigger that set that saga's whole plot in motion.

No one has laid eyes on the completed ship, yet the plans alone left Franky and Iceburg reeling, unable to fathom how anyone could ever build such a thing. Tom, reckoned the greatest shipwright in the world, judged it the most monstrous vessel any yard had ever turned out. Ranked the mightiest warship anywhere and rumored to sink islands with one blast, it would hand its master the power to seize control of the world.

The lasting hazard lies in the drawings, which outlived the ship's construction. Whoever holds them could raise a fleet of battleships every bit as ruinous as the first. Those plans were kept on purpose, a safeguard so a fresh Pluton could be built if the world ever had to fight the Ancient Weapons, the original included. With the blueprints now gone and the ship still dormant, that option no longer exists.

Water 7 both created the warship and inherited responsibility for its plans, which a chain of master shipwrights protected across generations before the drawings reached Tom, who then entrusted them to the two apprentices under him, Cutty Flam and Iceburg. A decade before the present day, Spandam of CP5 hunted the weapon, publicly framing it as a way to end the pirate age while privately intending to grab power for himself. His hunt dragged Tom, Iceburg, and the man later called Franky into ruin.

Far away, Crocodile pursued the identical goal, building Baroque Works and pressuring Nico Robin, the only surviving reader of the key Poneglyph, in an attempt to take it via Arabasta. Luffy's victory ended that plot. Years afterward, Franky, who had concealed the plans within his own body, set them ablaze before Spandam at Enies Lobby. In Wano, the former shogun Kouzuki Sukiyaki told Robin and Trafalgar Law where the ship rests, deep under Mt. Fuji, adding that the country's encircling walls would first have to fall before anyone could raise it.