The plot revolves around two non-hereditary brothers, Hidaka Shurato and Kuroki Gai, lifelong best friends who are polar opposites of each other in appearance and personality. While fighting each other in a martial arts tournament, they are suddenly encased in a beam of light and transported to a parallel world, Tenkuukai, where modern technology does not exist and instead the people rely on Sohma, a form of spirit energy, similar to the Force or Chakra.
Shurato discovers he is actually the reincarnation of an ancient king of the same name, who once ruled this world, and one of the "Hachibushu", a group of eight legendary warriors with large quantities of Sohma, and was brought here along with Gai to fight the Asura Gods, a legion of destructive warriors. However, for unknown reasons, Gai attempts to kill Shurato repeatedly, confusing Shurato as the real Gai is a pacifist and the most compassionate person he knows.
Things quickly go wrong when Shurato and another of the Hachibushu, Ten-Oh Hyuga, are framed for the petrification of Lady Vishnu, a powerful divinity and the leader of the people of Tenkuukai. The actual culprit, Vishnu's highest advisor and Asura spy Indrah, and the corrupted Gai manage to convince the remainder of the Hachibushu, as well as all of Tenkuukai's warriors and soldiers, that Shurato and Hyuga are evil and must be killed.
Although at first reluctant to get involved, Shurato eventually resolves to aid Hyuga in uncovering the conspiracy and cure Vishnu. They are accompanied by the young Tenkuukai spirit priestess Lakshu, and two others of the Hachibushu, Ryu-Oh Ryouma and Karura-Oh Reiga. Along the way, they engage in battle with the other four of the Hachibushu, sinister Asura agents in league with Indrah, and the majority of Tenkuukai's population.