In the world of Naruto, ninja can arm themselves with an astonishing variety of weapons and tools, far beyond the basic shuriken and kunai knives that one might expect. For instance, Sasuke Uchiha wields the electric Kusanagi and Kisame Hoshigaki of the Akatsuki organization is carries the bizarre chakra-eating sword, Samehada.
While many ninja in the series use a variety of organic tools, like Shino Aburame's chakra beetles, it may come as a surprise to some that the Samehada is alive. Samehada, though, is in a different league from any beetle swarm.
Samehada's Powers, Origin & True Nature
The exact origins of the Samehada are unknown. Was it created in one of Orochimaru's terrifying laboratories? Or was it a natural entity that morphed into a sword-like shape over time? It's not entirely clear, but Samehada's entered the ninja world when the first Mizukage owned it and passed it down to his successors. Much more recently, Mangetsu Hozuki acquired the Samehada as part of his collection, and later still, Fuguki Suizakan of the Seven Swordsmen owned Samehada, until Kisame killed him to obtain it. For years after that, Kisame and Samehada were master and minion together, until Killer Bee temporarily owned it after "killing" Kisame (the real Kisame was hidden the sword).
Samehada is a living thing that can think for itself, though it is never seen speaking, either with its mouth or telepathically. Instead, the Samehada expresses itself via its actions, and Kisame has figured out its preferences over time. The Samehada has a massive appetite for chakra and, though ambient chakra is safe from its maw, even if a ninja summons their biju cloak, the Samehada can eat it. The Samehada can't stand the heat of fire chakra, however. Once the Samehada starts eating, it will grow bigger, and if it faces a truly powerful foe such a Killer Bee, it will break free of its bandages and reveal its full size and mouth.
The Samehada is picky about the chakra it eats and who may hold it. Anyone deemed an unworthy wielder will have their hand impaled by spikes from its handle, and the Samehada might even squirm away. During combat, Samehada will allow itself to be swung around like a sword, but in case of emergency, it will actually bend and twist to evade enemy fire, such as during Kisame's fight with Killer Bee. During intense battles, the Samehada will even allow its wielder to fuse with it, and when Kisame does this, he assumes a shark-like form.
The Samehada can also store its owner inside, which is what Kisame did when he infiltrated the Hidden Cloud Village to gather intel. A white Zetsu, in Kisame's form, allowed Killer Bee and the Raikage to think that Kisame was dead, so they lowered their guard and took Samehada (with Kisame inside) to their village.
The Samehada's Use In Naruto
The Samehada first appeared in Naruto at the same time as Kisame and his partner Itachi Uchiha, shortly after Orochimaru's failed assault on the Hidden Leaf Village. During this time, Naruto was out adventuring with Jiraiya, and Itachi and Kisame cornered him in a motel. As Naruto readied an attack with Kurama's chakra, Kisame to swung the Samehada to instantly devour it. This left Naruto unable to perform even tiny jutsu, and Kisame boasted that Samehada could eat any chakra and render the opponent helpless. In an earlier battle, Kisame had merely used the tip of the Samehada to shred Asuma Sarutobi's arm, without revealing Samehada's chakra-eating ability.
Samehada's biggest fight was versus Killer Bee, when its true powers and nature were revealed at last. Bee could use incredibly strong biju cloaks with the Ox's chakra, but Kisame was able to steal it all with the Samehada, growing it to its full size (this was the white Zetsu Kisame). After this fight, Kisame snuck into the Hidden Cloud Village inside Samehada, and later, during an intense fight, he fused with it to wield enormous power. Kisame could even heal mortal injuries with the Samehada's stoken chakra, astonishing Might Guy and other Leaf ninjas. With Samehada by his side, Kisame was seemingly indestructible.
Later, after Kisame truly died, Killer Bee adopted the Samehada for real and use it during the Fourth Great Shinobi War. Few other ninja could have possibly proven worthy of that great (and unique) sword.