As we promised earlier, we'll be doing a series of individual articles on the three ancient weapons from Eiichiro Oda's One Piece series. In these individual articles, we'll be introducing each of the ancient weapons in more detail, revealing everything we know about each one. Our main article only revealed the basic details of the three ancient weapons and their powers and abilities, but in this series of articles, we'll be telling you everything we know about these weapons, as well as everything we know.

In this article, we will be introducing the Ancient Weapon Poseidon, the only currently confirmed living weapon among the three Ancient Weapons in One Piece.

Who is the ancient weapon Poseidon?

Poseidon was first mentioned when Nico Robin read the Skypiea Poneglyph. Recently, the king of the Ryugu Kingdom, Neptune, revealed that Poseidon is located on Fish-Man Island. This weapon is not an object, but a hereditary ability that only a few female members of the Fish-Man Island royal family develop every 100 years, according to Neptune himself.

A power inherited and awakened by Princess Shirahoshi, which consists of being able to summon, communicate with, and control the kings of the sea at will. The only mermaid princess who also possesses this ability is Princess Poseidon, who lived in the Void Age. Instead of being an inanimate object like usual weapons (except for weapons attached to Devil Fruits), Poseidon is a mermaid who belongs to the royal lineage of the Ryugu Kingdom.

After her death, her name was treated as a title given to a mermaid born into the royal family and possessing the same power she possessed in life. Nowadays, Shirahoshi has inherited the power and name of Poseidon from her. Anyone possessing this ability is called a Mermaid Princess. Poseidon has the power to communicate with and control the kings of the sea, an ability that even the most powerful merfolk cannot wield.

What are the powers of the ancient weapon Poseidon?

Poseidon is one of the Three Ancient Weapons, along with Uranus and Pluto, the latter possessing equal power and capable of destroying entire islands. Poseidon is a mermaid born every millennium or two, endowed with the power to control and communicate with Sea Kings. This power is considered a weapon since Sea Kings are so powerful that they can single-handedly destroy islands just to feed themselves.

However, when used for benevolent purposes, this power can save thousands of lives, as Shirahoshi used it to save the Fish-Men from Noah's fall. Shirahoshi is the heir to this fantastic power and awakened it during the fight between Luffy and Hody. She first used it unconsciously to save her mother, Queen Otohime, from a Celestial Dragon, by summoning the Sea Kings.

According to Otohime, the legend adds that Shirahoshi will be visited by a stranger charged with guiding his power on the right path, and it is at this time that the world will experience profound upheavals.

How was the ancient weapon Poseidon created?

Poseidon lived during the Void Century and made a pact with Joy Boy. She would use her powers to command the Sea Kings to bring the Noah to the surface and activate the planned mission, the details of which would be revealed when it was relocated. However, Joy Boy failed to engage her with Poseidon for unknown reasons.

After that, Joy Boy left his deed in an apology letter located in the Poneglyph of Gyojin Island, exactly in the Sea Forest of the Ryugu Kingdom. After the Void Century, Poseidon disappeared from the records, the only information available about him being the Shandora Poneglyph on Skypiea and the Fish-Man Island Poneglyph located in the Sea Forest, which is written as an apology letter from Joy Boy to Poseidon, apologizing for breaking his part of the bargain.

Even after his death, his power remained, and Poseidon's abilities were passed down through the generations of the royal family, even though he never awakened. Meanwhile, Fish-Man Island tried to keep its end of the bargain, even though Joy Boy didn't. The World Government spent the next few centuries trying to prevent the awakening of the ancient weapons by banning the reading of the poneglyphs.

The story of Poseidon became a legend on Fish-Man Island over time, and stories were passed down through the royal family of the Ryugu Kingdom. According to one such legend, a mermaid would be born with the ability to control the kings of the sea, and on that day a man would come to guide her. The first Vander Decken traveled to Fish-Man Island to find this mermaid.

However, he failed to find her, and the story is passed down from father to son, with each new Vander Decken attempting to find the princess. Eight years before the series began, Princess Shirahoshi unwittingly demonstrated her ability to summon Sea Kings while her mother was in danger of being slaughtered by the world noble Mjosgard. Her screams summoned a group of Sea Kings, allowing her mother and Vander Decken IX to discover her abilities.

At this point, Decken deduces that Shirahoshi is the legendary mermaid princess her family has been searching for and has decided to marry her to access her formidable abilities (as well as her unparalleled beauty), prompting him to send her marriage proposals, threatening the marriage for the next ten years. Otohime, knowing that such powers can be both beneficial and deadly, had to instruct her three sons to train hard to become powerful warriors in order to protect Shirahoshi when the time comes.

Shirahoshi's power was fully awakened during the fight against the New Fish-Man Pirates, which Neptune pointed out was not a good thing. In fact, when Caribou overheard Nico Robin and King Neptune discussing the Ancient Weapons and Shirahoshi as Poseidon, he quickly attempted to kidnap her for her apocalyptic power, but was stopped by the Straw Hats.