Seven Ninja Swordsmen of the Mist

The is an organization consisting of only the greatest blade wielding shinobi of their generation that Kirigakure can produce. There can only be seven members at a time, hence the name. According to Suigetsu, the swords of the Seven Swordsmen are passed down from generation to generation.

History
The members of the Seven Ninja Swordsmen were the people who came from the Bloody Mist's graduation exams with the greatest battle skills. However, the members also had a great lust for power, which led several of them to defect and become missing-nin. Kisame Hoshigaki became a member after killing his predecessor, who was revealed to be a traitor leaking information to the enemies, but Kisame later became the first of the seven to abandon Kiri after committing several unauthorized assassination, attempting to overthrow the government and then joined Akatsuki. Zabuza Momochi would later defect as well after a failed coup d'etat and assassination attempt on the Mizukage. Before leaving however, he encountered a boy named Haku with a unique kekkei genkai and took him with him, as well as the Demon Brothers, Gōzu and Meizu. Eventually, Chōjūrō became a member of the Seven Swordsmen of the Mist. However, he is implied to be relatively new to the group.

In the anime, it hasn't been confirmed when or why Raiga Kurosuki left Kiri, but it was around the same time when he discovered a boy named Ranmaru, who ended up having a similar relationship with Raiga to that of Zabuza and Haku. Ranmaru also had a special dōjutsu which Raiga used for his own purposes, furthering their similarity to Haku and Zabuza.

The Hōzuki brothers, Mangetsu and Suigetsu, both trained with the intention of joining the Seven Ninja Swordsmen together. However, their ambitions were cut short when Mangetsu died and Suigetsu was captured by Orochimaru. Suigetsu has since taken an interest in collecting all of the swords of the Seven Swordsmen for himself.

Shinobi World War Arc
During the Fourth Great Shinobi World War, Kabuto Yakushi used the Summoning: Impure World Resurrection to resurrect the previous generation of the Seven Ninja Swordsmen of the Mist to fight on behalf of Akatsuki. Zabuza being part of the group that attacked the Allied Shinobi Forces' Third Division, Gari and Pakura summoned the remaining six to the battlefield.

Known swords

 * A giant knife with a butcher-knife-like appearance, the wielder can use the hole on the blade to grab an opponent's head and decapitate them, hence the name. It has a detachable handle which makes it easier to carry around. Formerly owned by Zabuza, it was later retrieved by Suigetsu and damaged in a battle with Killer Bee, and was snapped in half by the Fourth Raikage. The half with the hilt was finally returned to Zabuza during the Fourth Great Shinobi World War. The sword has an ability to regenerate using the iron absorbed from the blood of those it cuts down.
 * The most terrifying of the seven blades, it has the appearance of a giant knife covered in shark scales. It also has the ability to "eat" chakra. Unlike other swords, it doesn't cut, but actually shaves ribbons of flesh off of foes just like shark's skin, another courtesy of the name. When fully revealed, the blade shows to have a chakra absorbing mouth at the end of it. Kisame can also absorb Samehada within his body turning him into a shark-like mutant creature. Spikes jut out of the handle when anyone other than the rightful owner tries to pick it up. Owned by Kisame after he executed the previous master but took a liking to Killer Bee because of his immense chakra; implied to be permanently Bee's after Kisame's suicide.
 * A bandaged double-handled sword that is capable of creating a chakra layer around itself in the form of a hammer. It is unknown if it is capable of forming other weapon types. It is currently owned by Chōjūrō.
 * Twin pikes that can be used to channel lightning release techniques. They can conduct lightning itself as well. They were formerly owned by Raiga, and fell to the bottom of a river in the Land of Rivers after Raiga killed himself. Currently, it has been summoned by Mangetsu Hōzuki to be used by its previous owner, Ameyuri Ringo. Imbued with lightning and is the sharpest sword forged.
 * Helmsplitter: A blunt sword consisting of a single sided axe and a hammer joined by a length of chain. Said to be capable of crushing any and all defense. This is done by first striking with the axe and then hammering it through the obstruction with the hammer. Wielded by Akebino Jin

Trivia

 * It seems to be a tradition for the members and aspiring members of the Seven Swordsmen to have sharpened teeth. All the known named members also have fruit-derived names. None of these hold true for the filler character Raiga, however.
 * Each one of the swords so far (except the anime-only character Raiga) seem to have a connection with fish. Kisame's sword Samehada is covered in scales, Chojuro's sword Hiramekarei is shaped like a fish and Zabuza's sword Kubikiri Hōchō looks like a butcher's knife, something commonly used to prepare fish for eating in Japan.
 * Several of the previous generation swordsmen have bandages around their necks. . The current generation has shown bandages around their swords instead.
 * At least three of the members became missing-nin, while one was discovered to be a traitor, leaking confidential information to other villages.