The Ancient Weapons are three legendary powers or devices from the Void Century, a period of history that has been erased from records by the World Government. These weapons are considered so dangerous that their mere existence could threaten the entire world.
In One Piece, there are three known Ancient Weapons: Pluton, a massive warship with unparalleled destructive capabilities; Poseidon, a living being who can command the Sea Kings—giant sea creatures capable of causing widespread devastation; and Uranus, the most mysterious of the three, whose nature and abilities remain largely unknown.
1. Pluton
Pluton is described as a massive and extremely powerful warship, capable of causing unprecedented destruction. It was constructed in the ancient past and is said to be the most dangerous battleship ever built. Pluton is rumored to be hidden somewhere in the world, and blueprints for its construction were passed down through generations of shipwrights in Water 7.
The blueprints for Pluton were safeguarded by the shipwright Tom, who passed them to his apprentices, including Franky, one of the Straw Hat Pirates. The World Government sought these blueprints, fearing that someone might attempt to rebuild Pluton and use it against them. However, Franky destroyed the blueprints to prevent them from falling into the wrong hands.
2. Poseidon
Poseidon is not a physical weapon but rather a person with the ability to communicate with and control the Sea Kings, giant sea creatures capable of causing widespread destruction. The title of Poseidon is inherited, and the current holder of this power is Princess Shirahoshi of Fish-Man Island.
Poseidon's power was intended to be used in conjunction with Joy Boy’s plan to relocate the inhabitants of Fish-Man Island to the surface. However, this plan was never fulfilled. The revelation that Shirahoshi is Poseidon makes her a significant figure in the world of One Piece, as her ability could potentially challenge the World Government or change the course of history.
3. Uranus
Uranus is the most mysterious of the three Ancient Weapons, as very little information about it has been revealed so far. Its nature, form, and capabilities remain unknown, but it is speculated to be as powerful as Pluton and Poseidon.
The lack of information about Uranus has led to much speculation among fans. Some believe it could be a weapon related to the sky or space, considering its name's mythological reference to the Greek god of the sky. Others suggest it could be a weapon of unparalleled destructive power, capable of threatening the entire world.