Naruto: Saisei Arashi/Jinchūriki and Tailed Beast

The Tailed Beasts (尾獣, bijū) are nine giant demons that serve to drive the plot of the Naruto series as well as in Naruto: Saisei Arashi. They are differentiated by the number of tails they have, with each possessing a number from one to nine. The tailed beasts are large, living forms of chakra, sometimes referred to as "Chakra Monsters" (チャクラのバケモノ, Chakura no Bakemono),[1] giving them power that far outmatches most shinobi. However, this immense strength is tempered due to their bestial nature, which restricts them from being intelligent enough to use it effectively. When a tailed beasts are sealed within a human, it is able to benefit from the knowledge of its host, giving it the ability to speak and better utilize its powers. Akatsuki has been capturing the tailed beasts and their hosts, and as of the Fourth Great Shinobi World War possess seven of the nine beasts. After the Fourth Great Shinobi War, the captured beast were released back into the world. In the universe of Naruto: SA, most of the beast have been resealed into stone idols that are worshipped as deities.

Jinchūriki
The jinchūriki (人柱力; Literally meaning "Power of Human Sacrifice") are humans that have a tailed beast sealed within them. They exhibit extraordinary powers, and in some cases are more powerful than their tailed beasts, because they have the intelligence to use the beast's powers effectively.

The first jinchūriki was the Sage of Six Paths, who sealed the Ten-Tailed Beast within himself to save the world, but before his death, the Sage divided the Ten-Tails' chakra into nine separate tailed beasts and sealed the Ten-Tails' body into the moon. During the Shinobi World Wars, the First Hokage, using his Wood Release techniques, gave several of the tailed beasts to the other shinobi villages as peace treaties, but when the First Hokage died, the villages had trouble containing the beasts. The Second Kazekage of Sunagakure was the first to research the jinchūriki, with the other villages following soon after, with hopes to use the beasts as weapons in human hosts, or in Konoha's case, keep the beasts from doing harm to their village. Each village has used a different seal when creating their jinchūriki. For example, the Fourth Hokage used the Four Symbols Seal, and Kumogakure's Killer Bee has an Iron Armor Seal. Akatsuki, an organization whose role in the first series was to capture the jinchūriki, used the Illusionary Dragon Nine Consuming Seals to extract the tailed beasts, and seal it away for future use.

In order to prevent the jinchūriki from turning traitor, it is tradition for the host to be selected from the family of the village's own Kage. In this way, the jinchūriki not only has strong ties of loyalty to village and their leader, but they also serve to show off the Kage's might. For example, Gaara is the son of the Fourth Kazekage, Killer Bee the brother of the Fourth Raikage.

The seal that keeps a tailed beast within its host is at its weakest when a female jinchūriki is in childbirth, due to the nurturing of the child in the womb using the power of the seal, weakening the seal in direct proportion. As such during childbirth, a ninja is required to keep the seal intact and also to restore the seal back to full power after the birth. A full term pregnancy for a female jinchūriki is about 10 months, presumably because the body has to nurture both the child and the seal simultaneously, as a result the child develops more slowly.

Jinchūriki are typically lonely people, viewed by those around them as the beast that has been sealed within them, leading to prejudice and being hated and feared. According to Akatsuki, the first two jinchūriki they captured loathed humanity, and their villages were in fact glad to be rid of them. However, certain jinchūriki refuse to waver, despite being shunned, instead having a cheerful demeanor, and eventually earning respect. Such examples are Killer Bee and Naruto Uzumaki.

As the jinchūriki draws on more of their beast's power, their personality tends to corrode into animalistic instincts. Because their survival depends on the safety of their hosts, the tailed beasts are very protective, and will act whenever their hosts' lives are in danger. Normally, these hosts have little control over themselves as they transform deeper into their tailed beast forms, and become more beastly in battle. However, jinchūriki that have full control of their tailed beasts can retain complete consciousness and control even after a full transformation.

Jinchūriki have access to a unique fighting style, depending on their tailed beast: Gaara controls sand, Yugito controls fire, Rōshi controls lava, Killer Bee can spit ink, and Naruto has high stamina, rejuvenation, and a large amount of chakra. By training, they can gain additional access to their tailed beast and its chakra, such as Killer Bee being able to synchronize with his beast, and transform himself into it. Not all jinchūriki can retain control when transforming into their tailed beast; when Naruto taps into his four-tailed form, he loses the ability to discern between friend and foe, and attacks anything in sight. A tailed beast can also provide its host with constant advantages, such as Gaara's self-activating Shield of Sand which automatically protects him, even from self-injury and Naruto's healing factor that immediately activates as soon as he incurs wounds.