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 Fuguki Suikazan, 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 assassinations, and attempting to overthrow the government, then joining Akatsuki afterward. 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 decided to take him along, as well as the Demon Brothers, Gōzu and Meizu. Since then, the total number of the group gradually decreased, as the swords one by one fell out of Kirigakure's possession. Eventually, Kirigakure was left with only one sword, and Chōjūrō became the only member of the Seven Swordsmen of the Mist.

According to a ninja from the Allied shinobi forces, the generation closest to the Fourth Great Shinobi World War was the strongest of the Seven Swordsman in the entire groups history, having been composed of the most powerful seven among the ninja that had ever been a part of this group.

The Hōzuki brothers, Mangetsu and Suigetsu, both trained with the intention of joining the Seven Ninja Swordsmen together. Mangetsu did eventually join, and mastered use of all seven of the swords, rather than one. However, he later died, and Suigetsu was captured by Orochimaru. Suigetsu now shows an interest in collecting all seven swords, in order to restore the group to its original power and become its new leader.

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.

Shinobi World War Arc
During the Fourth Great Shinobi World War, Kabuto Yakushi used the Summoning: Impure World Resurrection technique 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. Mangetsu then summoned most of the swords with a scroll, and most of the swordsmen got an advantage against the Third Division, being covered by Zabuza's Hidden Mist Technique.

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. The sword has an ability to regenerate using the iron absorbed from the blood of those it cuts down. It also 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, where it had since then regenerated a large portion of the blade.
 * The most terrifying of the seven blades, it has the appearance of a giant knife covered in shark scales. It is a sentient, living, weapon and 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 merge with Samehada, 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. It was owned by Kisame after he executed its previous master, Fuguki Suikazan, but has recently bonded with Killer Bee because of his immense chakra.
 * A bandaged double-handled sword that is capable of creating a chakra layer around itself in the form of a hammer. It is currently owned by Chōjūrō.
 * Twin pike-like "bolt" swords that are imbued with lightning which increases their cutting power. They are said to be the sharpest swords ever forged. Wielded by Ameyuri Ringo. However, in the anime, they were introduced earlier, in the possession of Raiga Kurosuki.
 * 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 defenses. This is done by first striking with the axe and then hammering it through the obstruction with the hammer, using the axe as a wedge. Wielded by Jinin Akebino.
 * A longsword in the shape of a needle with long thin wire that resembles thread. This sword can pierce multiple enemies in succession and stitch them together in large bundles. Wielded by Kushimaru Kuriarare.
 * The "explosion" sword that has a scroll full of exploding tags incorporated into it, lined up behind the blade, combining swordsmanship and explosions. Once the tags detonate the scroll seems to roll up so only the enemy is caught in the blast while the wielder can launch another explosion with another set of tags. Wielded by Jinpachi Munashi.

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 anime only character Raiga, however.
 * 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.
 * Although Mangetsu was said to have mastered use of all the swords, other members of his generation wielded 6 of them, likely leaving Hiramekarei as the blade he could exclusively use.
 * Two members of the Seven Swordsmen (three in the anime) were former ANBU members.