Kokuō

Kokuo takes the form of a white horse fused with the head of a dolphin. Long, pointed horns rise from its head, joined by a set of shorter horns at the front, three in the manga and two in the anime. The tips of its horns, hooves, and tails carry a tan coloring, with matching spots preceding the tan patches, and reddish markings sit below its deep blue-green eyes. In the earliest days of its existence it was far smaller, and its horns had yet to grow to their full length.

Reserved and softly spoken, Kokuo rarely says much, and when it does refer to itself it uses an antiquated, formal pronoun that lends its speech a courteous air. For all its quiet, it holds genuine pride as a tailed beast and was pained at being reduced to a controlled puppet during the Fourth Shinobi World War. Once the fighting ended, it announced its wish to withdraw into the forest and live apart, a choice that paints it as a peace-seeking creature with no appetite for further conflict.

Kokuo's resolve is remarkable, and it stood alone among the captured beasts in briefly wrenching itself loose from Tobi's grip to lash out at him. Its body carries tremendous strength, and it fights with its horns, ramming with force enough to hurl the Eight-Tails a great distance. As a tailed beast it holds an immense store of chakra along with potent healing, mending wounds in itself and others within seconds, and it is essentially deathless, returning in a younger shape whenever it is slain. It can form a Tailed Beast Ball, and by fusing water and fire chakra it produces Boil Release, raising its chakra to scalding temperatures. That power underlies the steam-based techniques that grant crushing physical might, filling its user with billowing vapor.

Its story stretches back to the final days of Hagoromo Otsutsuki, who divided the Ten-Tails' chakra into nine named beings and foretold that they would one day reunite and meet the one destined to teach them true strength. Generations later, Hashirama Senju handed Kokuo and Son Goku over to the Hidden Stone as a gesture of goodwill, and the beast was eventually sealed inside Han before Akatsuki tore it free. During the great war it was forced to serve as Tobi's weapon, yet it introduced itself to Naruto within a deeper layer of the beasts' shared consciousness and later affirmed that he was the child the Sage had spoken of. Freed at last after Kaguya's defeat, it lent Naruto its power and chose seclusion, and in the new era it declined to seek human protection against Urashiki, still wary of being seized and exploited once more.