Saiken

Saiken, more commonly known as the Six-Tails, is one of the nine tailed beasts. It was last sealed within Utakata of Kirigakure. Saiken and the tailed beasts first came into being in the waning days of Hagoromo Ōtsutsuki, who used his Creation of All Things Technique to divide the Ten-Tails' chakra into nine separate bodies and giving each a name. Some time after being created, the Sage explained to the young tailed beasts that a link existed between them despite their separation. He also foretold of a day when they would be brought together again - though not as they were - and that at that time someone would emerge to show them what true power is. After Hagoromo's death, the tailed beasts drifted apart, apparently due to Kurama's belief that their number of tails was an indication of their strength. Saiken eventually fell into the possession of Kirigakure and was sealed into Utakata.

In the anime, it was revealed that at some point before his appearance, Utakata's master, Harusame, tried and failed to remove Saiken from within Utakata, intending to save his student from being a living weapon for his village. Utakata, however, having not heard what his master had said to him, later came under the assumption after the incident that his master had tried to kill him. This failed removal resulted in Utakata transforming into Saiken and killing Harusame. Though much has not been seen of Saiken's personality, the giant slug uses "ore" when referring to itself, "ore" being a boastful way of saying "I". It also speaks with a dialect which may possibly be Ōsakaben in origin. In the anime, Saiken also seemed to be kinder and not as self-serving and malicious as most other tailed beasts, as when Utakata asked for its help to save Hotaru it seemed to willingly comply; and later it simply receded back into Utakata without trying to take him over. However it was not above killing for self preservation, as seen when it killed Harusame when he attempted to extract it from its jinchūriki. In the anime, it speaks with a high pitched voice and appears to be very energetic. Saiken resembles a large white, with a slight light blueish tint, bipedal slug with stubby arms and feet. It has two prominent optical tentacles (eyes) and hole-like openings as a mouth. Its entire body is covered in a slimy substance. During the last remaining days of the Sage of Six Paths, Saiken was much smaller than its present-day self, but was still much larger than the Sage. As a tailed beast, Saiken has a massive amount of chakra and can use it to create a Tailed Beast Ball. Saiken has shown the ability to emit corrosive substances that can instantly disintegrate its target on contact in the form of liquid or gas. It has tremendous durability, able to withstand being thrown a great distance by Kurama. Saiken possesses an affinity for Water Release. It can expel a sticky, slime-like substance from its mouth, which is capable of trapping its targets.

In the anime, in an attempt to stop the Fury technique from causing untold destruction, Utakata went into his full Six-Tails form to shield the blast. Later, Utakata was confronted and captured by Nagato's Six Paths of Pain. Afterwards, Saiken was extracted from Utakata's body, being sealed into the Demonic Statue of the Outer Path, thus killing the jinchūriki in the process. After Utakata's full transformation into Six-Tails, he attacks Kakashi and Guy, emitting a corrosive alkali from its mouth, which Kakashi warned Guy not to touch. After Guy dissipated the gas with his Morning Peacock technique, the Six-Tails prepared to attack him again. After Son Gokū was resealed into the Demonic Statue of the Outer Path, Tobi, who was intent on going all-out from that point on, forced Utakata to fully transform into the Six-Tails. The opposing tailed beasts prepared to attack the shinobi, but they were rebuffed by a fully-transformed Naruto. Wasting no time in their attacks, the Six-Tails incapacitated Naruto and Kurama by swallowing the arm, but the slug was slammed into the Two-Tails, sending them both flying away. The opposing beasts regrouped and then prepared a collaborative Tailed Beast Ball, which was met by one from Naruto and Kurama. As Naruto entered a deeper plain of the tailed beasts' consciousness, Saiken introduced itself to the young shinobi. Later, as Saiken was freed from the chakra receiver, it affirmed Kurama's belief that Naruto was the person the Sage of the Six Paths had spoken about so long ago before being resealed back into the Demonic Statue. Saiken appeared alongside with the other tailed beasts with the exception of Gyūki and Shukaku when the Ten-Tails looked down at Naruto. The image of the tailed beasts, along with a silhouette of the Sage of the Six Paths, drove the Ten-Tails to a fit as it evolved further. Later on, the Allied Shinobi Forces managed to pull the tailed beasts out of Obito, thereby freeing them, including Saiken. When Madara ran towards the tailed beasts, both Shukaku and Gaara conjured numerous sand bullets and were able to restrain the Uchiha's movements. Using the opportunity to attack, the tailed beasts each took a swing at their opponent, giving sand-manipulating duo an opening to use their Desert Layered Imperial Funeral Seal, but Madara managed to escape the sand pyramid with his Susanoo. As Naruto in Tailed Beast Mode pinned Madara down with a tail, Saiken and the other tailed beasts joined in and did the same to increase the damage, but the Uchiha survived their attacks and retreated to a safe distance. After he received his own right Rinnegan eye from a White Zetsu clone, Madara quickly summoned the Demonic Statue of the Outer Path from Obito's body, and used the Rinnegan to repel the tailed beasts. With the tailed beasts stunned, Madara then chained them up and sealed them back into the Demonic Statue. Later, the chakra Saiken transferred to Naruto earlier, manifested within Naruto's subconscious along with the other tailed beasts to speak with the young jinchūriki and the spirit of Hagoromo Ōtsutsuki. There, they all voiced their shared belief to the Sage that Naruto was the child of prophecy.