Saiken

Saiken (犀犬, Saiken), more commonly known as the Six-Tails (六尾, Rokubi), is a tailed beast sealed within Utakata of Kirigakure. Saiken was one of the Tailed Beasts.

Background
Saiken first came into being in the waning days of the Sage of the Six Paths, who used his Creation of All Things ability to separate the Ten-Tails' chakra from its body and divide it into nine separate constructs in order to ensure that it would never resurface after his death.[2][3] Some time after being created, the Sage sat down with all the young tailed beasts and told them that they would always be together even when separated, and that one day they would become one entity again with different names as well as forms than they did then when the time came for them to understand what true power is.[4]

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.

Personality
Though much has not been seen of Saiken's personality, the giant slug uses 'ore' (オレ) 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.

Appearence
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 the Six Paths, Saiken was much smaller than its present-day self, but was still much larger than the Sage.[4]

History
It starts out when Hotaru and her guardian, Tonbee, are being attacked at their mountaintop fort. Utakata and Hotaru escape with En no Gyōja's secret kinjutsu, while Tonbee tries to hold off the attackers, but was easily defeated, and the attackers, the Magaki Group, go after them. Team Yamato are assigned by Tsunade to go and protect Hotaru on her way to the Tsuchigumo village. When the team find the fort, they saw Tonbee, who has been viciously attacked by the four-man bandits. Sakura stays and heals Tonbee, while Naruto, Sai, and Yamato follow Utakata and Hotaru. Naruto catches up to Utakata and Hotaru, and Utakata attacks Naruto with some of his Soap Bubble Ninjutsu. After Utakata learned that they are not attackers, he entrusts the protection of Hotaru to them. Hotaru's uncle betraying her to the Magaki Group, but when they think that they have found the hidden scroll, it turns out to be a bomb. Hotaru escapes, and she meets up with Utakata in the forest. He faces off against the bandits again, and quickly flees. After Utakata escaped with Hotaru, the bandits were confronted by their leader, Shiranami. He showed them that Utakata was a missing-nin from Kirigakure with a bounty of 50 million ryō. Akaboshi asked their leader what they should do, which he began to muse about.

When Hotaru and Utakata were alone, Utakata was about to leave Hotaru again, but Hotaru, trying to convince him not to leave her alone, partially took off her shirt, showing him something on her back that shocked him.

All of a sudden, the Kirigakure ANBU found Utakata and wrapped him up with their Water Release: Water Whip technique and began subduing him with their Lightning Release: Electromagnetic Murder. The captain revealed to Hotaru, who he was holding hostage, that Utakata was in their Bingo Book, and was wanted for killing his master. Naruto and his team arrived and managed to loosen one of the water whips holding Utakata. Both parties began to fight, but the leader of the Kirigakure ANBU appeared, and discussed the situation with Yamato. Due to Hotaru's insistence to be with Utakata, it was agreed that Utakata stayed with Team Yamato and they wouldn't hunt him until she was safe, but afterwards, they'd resume tracking Utakata down. Tsurugi, the leader, asked Utakata to return to Kirigakure, saying that the village changed, no longer earning the nickname of Village of the Bloody Mist. Utakata refuses, and says that he'll keep doing as he pleases.

After the groups part ways, Hotaru begins hurting from an injury sustained during the earlier altercation. Utakata has Naruto collect medicinal herbs. When Naruto returns, he witnesses what was done to Hotaru's back, where her clan's kinjutsu was put. Utakata voices his absolute disdain for people who selfishly take advantage of people's loyalty, only to treat them as tools.

Everyone is shocked to learned that Hotaru actually requested for the technique to be sealed in her. After she explained that she wanted her grandfather's dream to restore their clan's glory to come true. When Tonbee voiced his sorrow that by now the clan had probably lost too much strength to ever return to such a status he suggested they end the potential danger of the kinjutsu by destroying it. Utakata was surprised that Hotaru's grandfather had created a way to safely remove it from Hotaru's body. When Tonbee insisted that no true master would do such horrific things without a way to undo them, Utakata wondered if the same was true for his master. Utakata resolved to find Tsurugi again to learn some answers about his late master.

Hotaru initially refused the idea to destroy the kinjutsu, feeling that it would make all her grandfather's efforts for nothing, but Utakata made her see that she couldn't restore their clan with such a destructive technique. While willing to accept this decision as a final act, she offered one other possible solution, to search for a man named Shiranami, who is an immensely gifted ninja who studied En no Gyōja's teachings and could be of great help. It was then decided that Naruto would attempt to find the man in two days while preparations for removing the kinjutsu were made.

When Naruto Uzumaki sought out Shiranami, the Magaki leader, who believed the latter was an ally, the Magaki Group ambushed Naruto and used Infinite Embrace to drain his chakra. While Chūshin beat Naruto, Benten almost revealed their plan before Akaboshi silenced him. Angered at being deceived, Naruto unleashed the Nine-Tails' chakra and broke out of the Infinite Embrace. Though shocked at Naruto's strength, the Magaki used their Multiple Infinite Embraces to crush Naruto. Much to their shock, however, Naruto was still able to resist, but not for long.

Later to Hotaru's dismay, Utakata suddenly leaves. Not wanting him to leave her, Hotaru goes off to find him. Along the way, she runs into Shiranami himself. He sympathises with Hotaru's loneliness and desire to restore their clan. After being convinced not to destroy the technique, she decides to write a message to Utakata. However, Shiranami reveals his true colours and knocks out Hotaru, taking her back to the Tsuchigumo village.

When Utakata is unable to find Tsurugi he finds Hotaru's messenger bird with a note for him. While it is from Hotaru saying she found Shiranami, Utakata is still at unease, feeling something is wrong. He goes to the location Hotaru wrote and finds that Shiranami is actually the leader of the bandits who trapped Naruto in a fūinjutsu. Utakata then uses his tailed beast chakra to scare the bandits and make them run.

Afterwards, he and Naruto track Shiranami back to Hotaru's village, where it is discovered that Shiranami took control of the villagers with his technique. The villagers attacked Utakata and Naruto and they were also confronted by the Magaki Group. Just before things got worse, the rest of Team Yamato arrived while hunting for Hotaru. Yamato, Sai and Sakura were fighting the villagers and the Magaki Group, while Naruto and Utakata were trying to save Hotaru from Shiranami. In the end Naruto and Utakata manage to save Hotaru and Team Yamato parts ways with Hotaru and Utakata. Hotaru and Utakata decide to leave Hotaru's village and travel around while Utakata trained Hotaru to make her stronger.