What Are the Ancient Weapons in One Piece? Pluton, Poseidon and Uranus Explained

One Piece has three Ancient Weapons: Pluton, Poseidon and Uranus. Their names sound like a set of legendary cannons, but they are not three identical machines. One is a warship hidden beneath Wano, another is a living mermaid princess, and the third remains a major mystery. Understanding that difference makes the stakes of the Final Saga much clearer.

The most important distinction is between what Eiichiro Oda has actually revealed and what readers have inferred. The Egghead arc connects an Ancient Weapon to the destruction of Lulusia, but it does not give us a complete technical description of Uranus. This guide separates confirmed information from theories instead of treating every popular guess as established canon.

Manga spoiler warning: this article discusses revelations from Fish-Man Island, Water 7, Wano and Egghead, including Vegapunk's broadcast. Anime-only viewers who have not reached those arcs may want to return later.

What are the three Ancient Weapons?

The Ancient Weapons are legendary powers linked to the world's suppressed history. The three known names are Pluton, Poseidon and Uranus, and each is potentially catastrophic in the wrong hands. The World Government fears knowledge of the lost past, while pirates and political figures have tried to locate the weapons for their own purposes. The weapons are part of the larger Void Century mystery, not a separate collection of ordinary pirate treasure.

Here is the short version: Pluton is an extraordinarily destructive battleship associated with Water 7 and now hidden beneath Wano. Poseidon is Princess Shirahoshi's inherited ability to communicate with and command the gigantic Sea Kings. Uranus is the third named weapon, but its form, location and precise capabilities have not been directly established. All three are dangerous, yet only two have clear identities in the story.

Pluton: the ancient battleship beneath Wano

Pluton enters the plot through the Alabasta storyline, when Crocodile seeks its location because he believes possessing the weapon would give him overwhelming military power. The Poneglyph in Alabasta contains information about it, and Nico Robin becomes central to the search because she can read the ancient script. Importantly, the weapon is not simply sitting in the Alabasta desert waiting to be uncovered.

Water 7 adds a second piece of the puzzle. The shipwrights preserved construction blueprints for Pluton, allowing the possibility of building another vessel if the original ever became a threat. Those plans passed through the hands of Tom, Iceburg and Franky. Franky's decision to burn them during Enies Lobby removes the obvious route to making a duplicate, but it does not destroy the original ship.

Wano finally answers the location question. In chapter 1055, Kozuki Sukiyaki tells Robin and Law that Pluton lies below the old, submerged part of Wano near Mount Fuji. He also explains that opening Wano's borders literally involves bringing down the enormous walls around the country. Doing so would release the ancient ship, but it would also expose Wano to danger. This gives Momonosuke's decision to delay opening the borders a practical dimension.

What remains unknown is the ship's exact appearance, its operational requirements and who could control it if it were released. It is reasonable to expect a warship with extraordinary firepower, but elaborate diagrams and claims about its specific weapons should not be presented as confirmed facts. Pluton's location is known; its full capabilities are not.

Poseidon: why Shirahoshi is an Ancient Weapon

Poseidon overturns the assumption that every Ancient Weapon must be built from metal. During Fish-Man Island, Robin's discoveries and her conversation with King Neptune reveal that the name belongs to a mermaid princess who can communicate with the Sea Kings. The present bearer is Shirahoshi. She is not a battleship, and the ability is not a Devil Fruit power.

The Sea Kings are colossal creatures that live in the oceans, and Shirahoshi's power can call and direct them. During the crisis involving the enormous ship Noah, their intervention demonstrates why that ability could change the fate of an entire island. It also suggests possibilities beyond destruction. A power capable of commanding creatures of that scale could be used to protect people, move a vessel or threaten a fleet, depending on the choices of its bearer.

Poseidon is associated with a previous mermaid princess from the distant past, and Joy Boy's promise to Fish-Man Island is connected to that history. However, the story does not establish that Shirahoshi automatically knows the entire ancient plan. Her power and her understanding of its significance are different things. Treating her only as a weapon also misses a central point of the arc: she is a person whose safety and freedom matter.

For readers comparing One Piece's different power systems, Poseidon is a useful reminder that not every supernatural ability belongs in the same category. Devil Fruits follow one set of rules; Shirahoshi's inherited connection to Sea Kings is something else entirely.

Uranus: the Ancient Weapon we still cannot identify

Uranus is named alongside the other two weapons, notably in Robin's discussion with Neptune in chapter 650. Beyond that, the manga has kept its physical nature and method of use obscure. The name's association with the sky has encouraged theories about a flying weapon, a weather system or an airborne machine, but a mythological name alone cannot confirm its design.

This uncertainty is important because discussions of Uranus often jump straight from a compelling theory to a definitive claim. The series gives us strong reasons to suspect a connection between an unidentified Ancient Weapon and the attack on Lulusia. It does not explicitly label the attacking device Uranus in the key Egghead explanation. Until the story does, the identification should be described as a theory rather than a settled reveal.

Was the weapon that destroyed Lulusia Uranus?

The Lulusia incident changes the scale of the Ancient Weapons mystery. An attack erases the kingdom and is followed by consequences that affect the wider world. Later, Vegapunk explains that a portion of his Mother Flame was stolen and that he believes it powered an Ancient Weapon used in the catastrophe. His account is central to chapters 1115 and 1116, and the anime adapts the revelation during Egghead.

Many readers conclude that the weapon must be Uranus because Poseidon is already identified as Shirahoshi and Pluton is sealed beneath Wano. That is a coherent inference, not proof of the device's identity. The story has not yet supplied a definitive nameplate, design or technical explanation for the instrument used against Lulusia. The safest answer is that the Lulusia attack is linked to an Ancient Weapon, while the Uranus identification remains unconfirmed.

This also means it is misleading to say that Imu's personal powers and the Ancient Weapon are necessarily the same thing. The narrative places the attack within the World Government's hidden exercise of power, but questions about the weapon's operators, control system and original creator still require direct answers.

Is the Mother Flame itself an Ancient Weapon?

No. Vegapunk describes the Mother Flame as an energy source he developed, not as a fourth named Ancient Weapon. His intended goal was to provide extraordinary energy for human progress. A stolen portion was then used, according to his deduction, to power a weapon capable of mass destruction. The distinction between a power source and the device consuming that power is the key to understanding Egghead's revelation.

This matters for the moral conflict around Vegapunk. Inventing an energy source does not mean he set out to erase a country, yet he accepts responsibility for the consequences of its theft and misuse. It also raises a frightening question for the wider world: if an ancient device can be activated again with a modern fuel source, its danger is not limited to an event eight centuries in the past.

How are the Ancient Weapons connected to the Void Century?

The Void Century is a gap in the world's recorded history, and the Ancient Weapons are among its most consequential surviving mysteries. Vegapunk's broadcast suggests that the ancient conflict reshaped the planet and that the catastrophic rise in sea levels was not simply a natural event. The weapons therefore connect historical censorship, geography and the present struggle for power.

The Roger Pirates reached Laugh Tale and learned truths that the rest of the world still lacks. Joy Boy's decisions also remain central: Vegapunk points to the preservation of the weapons for later generations without claiming to understand all the reasons. The crucial unanswered question may not be who can destroy the most territory, but why such terrible powers were left for the future at all.

This is also why the Ancient Weapons cannot be reduced to a conventional power ranking. Poseidon could command living creatures, Pluton is an engineered vessel, and Uranus remains unidentified. Their uses and limitations are too different, and too incomplete, to declare a reliable winner. The same unresolved history gives added meaning to the Will of D, another long-running mystery tied to the world's future.

Could the Ancient Weapons change the ending of One Piece?

They almost certainly matter to the story's endgame, but the exact role of each remains open. Pluton is tied to the decision to open Wano. Poseidon connects Fish-Man Island, Noah and the Sea Kings to an ancient promise. The unidentified weapon associated with Lulusia demonstrates that the danger is not merely theoretical. Those threads point toward choices about protection, freedom and the control of destructive technology.

A useful way to follow future chapters is to ask three questions whenever a new clue appears: does it establish the weapon's identity, does it reveal how the weapon works, or does it only suggest who might possess it? Keeping those categories separate prevents speculation from hardening into false certainty. The Elbaph story setup may add context to the larger history, but no single theory should be treated as canon before the manga confirms it.

What we know and what remains a mystery

Confirmed: there are three named Ancient Weapons; Pluton is a battleship hidden beneath Wano; Shirahoshi is the current Poseidon; Uranus exists but its form is unresolved; and Vegapunk connects stolen Mother Flame energy to an Ancient Weapon used at Lulusia. Unconfirmed: Uranus's precise identity, the full design and operation of Pluton, the complete history of the weapons during the Void Century, and the purpose for which Joy Boy wanted them preserved.

The distinction is what makes the Ancient Weapons compelling. They are not simply three prizes for the strongest pirate to collect. They are evidence that the present world was shaped by choices made long ago, and that future characters may have to decide whether inherited power should be used, hidden or dismantled. The answer will matter far beyond a single battle.