Kurama - Nine Tails

Kurama more commonly known as the Nine-Tails, is one of the nine tailed beasts. Centuries of being sought after as a tool for war and regarded as a monster that felt no emotions and deserved none in return caused Kurama to hate humanity. After being sealed into Naruto Uzumaki, Kurama attempts to maintain its negative opinions about the world, but with Naruto's insistence on treating it with respect, the fox overturns its hatred and willingly strives to use its power for the world's salvation.

Kurama 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 that would come to be known as tailed beasts in order to ensure that it would never resurface after his death. 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 and forms than they did. Then, when the time came, they would know what true power is. Over the centuries, Kurama has gained a reputation as an age-old natural disaster, appearing suddenly out of nowhere to attack areas that have been breeding grounds for the darkest aspects of human nature. Kurama Swallows Kinkaku and Ginkaku

At one point during the time of the formation of the shinobi villages, the Gold and Silver Brothers of Kumogakure were assigned to capture Kurama, but were both swallowed whole by the fox. However, the two brothers managed to survive and gain some of its power by eating the flesh of its stomach for two weeks, forcing Kurama to regurgitate them.Hashirama vs Madara

The battle between Madara and Hashirama, with Kurama under Madara's control.

After that event, Madara Uchiha defected from Konoha and used his Sharingan to control and use Kurama to help him fight against Hashirama Senju, the First Hokage, in order to exact his revenge. During their battle, Madara combined his Susanoo with Kurama, increasing the latter's offensive and defensive capabilities. However, Hashirama was able to remove Kurama from Susanoo and released the tailed beast from Madara's control, subduing it in the process. After his victory over Madara, Hashirama deemed Kurama too dangerous to be allowed to walk free and Mito Uzumaki sealed the fox within herself, becoming its first jinchūriki.

Over the period of time which included the first two Shinobi World Wars, Mito kept Kurama at bay except for one occasion when the seal had weakened as she was going through childbirth. Toward the end of her life, Mito passed on this status and responsibility to another member of her clan, Kushina Uzumaki, who later became the wife of Minato Namikaze, the Fourth Hokage. Although Kushina was terrified with the responsibility of containing Kurama, Mito assured her successor that the fox's hatred was powerless against her love. Kurama sealed within Kushina

Kurama, sealed within Kushina.

Twelve years before the start of the series, after the end of the Third Shinobi World War, the Third Hokage and his wife made preparations to ensure that Kurama would remain sealed within Kushina as she gave birth to Naruto. However, despite keeping her childbirth a secret, a masked man discovered Kushina's location, killing her escorts and managing to break the seal, seizing control of Kurama. Since Kushina survived the extraction, the masked man tried to have Kurama kill her before Minato got her and their son to safety. Soon afterwards, the masked man summoned Kurama into Konoha and ordered it to destroy the village. Konoha's destruction by Kyuubi

Kurama attacks Konoha.

While Kurama was rampaging in the village and decimating the shinobi forces that tried to repel it, Minato managed to place a Contract Seal on the masked man during their fight to free the fox from the masked man's control. Despite that, Kurama still harboured a deep hatred for Konoha for sealing it away for decades and resolved to destroy the village without orders from the masked man. Before Kurama could annihilate Konoha, Minato summoned Gamabunta on top of the fox, and quickly teleporting it to Kushina and Naruto's location, while letting its Tailed Beast Ball detonate away from the village. Soon afterwards, Kushina used her chakra chains to subdue Kurama, planning to seal it back inside her before she dies. However, Minato, knowing that Kurama would revive without a host, and how great a threat the masked man is, came up with a plan to give Naruto the means to combat the masked man in the future when he decides to attack again. Nine-Tails ep

Yang-Kurama, moments after being sealed within Naruto.

Since Kurama's chakra was too immense to be sealed within an infant like Naruto, Minato first used the Dead Demon Consuming Seal to separate and seal its Yin half within himself and then prepared the Eight Trigrams Seal to imprison the Yang half within Naruto. With the chain loosening from the fox's reduced size and Kushina weakened, it attempted to stop the process by killing Naruto, but both of the parents sacrificed themselves to protect their newborn child and completed the sealing. Later, upon awakening within Naruto's subconscious and learning the nature of the seal, Yang-Kurama quickly realised the situation behind Minato's intention. However, it calmly decided to wait and weaken the seal through the cracks of its formation with its chakra, determined to influence Naruto as much as it can to use its power.

In the anime, it was revealed that Kurama had left behind large amounts of its chakra during the attack. Kazuma collected and sealed the chakra within his own son, Sora, hoping to make use of its power for his own agenda.