The Ancient Weapons Explained: Pluton, Poseidon & Uranus
Three weapons powerful enough to end the world, surviving from the Void Century. One is fully revealed, one is confirmed to exist and hidden, and one is still almost a total blank — here's the difference, and why it matters.
The Ancient Weapons are three world-ending powers left over from the Void Century, and the World Government's fear of them shapes a huge amount of the plot: whoever controls all three could, in theory, dictate terms to the entire world, which is exactly why the Government has spent centuries trying to locate and control them quietly rather than destroy the idea outright.
The names themselves are a clue fans lean on heavily — Pluto (god of the underworld), Poseidon (god of the sea) and Uranus (god of the sky) form a classical land/sea/sky triad, which is why most fan theories about the unrevealed weapon assume a sky-based power even though the story hasn't confirmed that reading.
Poseidon — the one weapon fully revealed
Poseidon isn't a machine at all; it's a bloodline. The current Mermaid Princess, Shirahoshi, is confirmed as Poseidon reborn — able to command the giant Sea Kings that patrol the Grand Line's depths. This is fully confirmed in the text, and it ties the weapon directly to Fish-Man Island's history and to Joy Boy's old, unkept promise, which is part of why her storyline carries more weight than her comic relief presence first suggests.
Pluton — confirmed to exist, not yet seen
Pluton is an ancient warship said to be capable of levelling an island in a single shot. Its blueprints are confirmed to have passed down through generations of Water 7 shipwrights — which is why Franky once held them, and why Water 7's shipwrights are treated as far more significant to the wider plot than a simple hometown-arc location would suggest. The ship itself has never been shown, but is heavily implied to be hidden in Wano, tied to the Kozuki family's history.
Uranus — genuinely the least understood
Uranus is the one weapon the story has said almost nothing concrete about, so nearly everything written about it anywhere, including here, is theory rather than fact. Beyond the sky/sun-themed guesses the naming convention invites, some fans connect it to Im and the Empty Throne on the logic that the Government would keep its most dangerous asset closest to its most hidden ruler — an elegant theory, but entirely unconfirmed.
Why having all three matters more than having one
The story frames the danger as cumulative: a single weapon is a serious regional threat, but the alliance that ended the Void Century is implied to have either used or controlled all three at once, which is a different scale of power entirely. That's likely why the Government tolerates Pluton and Uranus staying lost rather than racing to recover them — reuniting all three under any single faction, including their own, may be the actual nightmare scenario.
FAQ: the Ancient Weapons
What are the three Ancient Weapons? Pluton (a battleship), Poseidon (a person who commands Sea Kings) and Uranus (still almost entirely unrevealed).
Who is Poseidon in One Piece? Shirahoshi, the Mermaid Princess of Fish-Man Island — this is confirmed in the story, not a theory.
Where is Pluton? Confirmed to exist, with its blueprints traced through Water 7's shipwrights; the ship itself is heavily implied but not confirmed to be hidden in Wano.
What is Uranus, and where is it? Unknown. Theories lean sky/sun-themed based on the Pluto/Poseidon/Uranus naming pattern, but the story hasn't confirmed its nature.
