Kokuō (Kai)

, more commonly known as the, is a tailed beast sealed within Han from Iwagakure. It has been captured, extracted, and sealed by Akatsuki. In the anime, Kokuō is indicated to have been one of the two tailed beasts that Akatsuki captured before the start of Part II. It was later resealed into a reincarnated Han during the Fourth Shinobi World War.

Background
Kokuō 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. 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. Kokuō eventually fell into the possession of Iwagakure and was sealed into Han.

Personality
Kokuō seems to be a quiet and reserved individual. Though it does not speak much, Kokuō uses the rather old-fashioned when referring to itself, causing it to come across as very polite.

Appearance
Kokuō primarily resembles a white horse, but with a dolphin's head. It has two pointed long horns and three shorter horns in front. The ends of its horns, hooves, and tails are light brown, with some of the same-coloured spots before the brown areas of its horns and hooves. It also has red markings under its dark blue-green eyes. During the last remaining days of the Sage of the Six Paths, Kokuō was much smaller than it is now and its horns were also shorter.

Abilities
As a tailed beast, Kokuō has a great amount of chakra and is able to use it to create a Tailed Beast Ball. Kokuō uses its horns in combat, it has shown enough ramming-force to even injure Gyūki and knock it a considerable distance away.

Trivia

 * literally means 'respectful king'. This name probably comes from the name of the tenth-century-ʙᴄ Chinese . He's famous for the legend surrounding his visit to the sacred, where he visits the goddess so he can eat from her peaches of immortality. There is also an account of the King being shown a human-shaped automaton — a completely artificial, fully functional robot with internal organs and all. This might tie into Han's appearance and abilities. In Japanese, the name '穆王' is pronounced as 'bokuō', so the unusual 'kokuō' pronunciation used for the beast's name was probably meant to bring the word  to mind.
 * The kanji '穆' in Kokuō's name comes from the archaic adjective, which means 'peaceful and lovely' or 'humble and dignified' and are also traits often associated with horses and dolphins.
 * According to Kishimoto's words from the second Naruto artbook, he tried to do a mix of a dolphin and a horse.