Kokuoh is Raoh's giant horse.
He is first seen when Raoh appears in Mamiya's village. Rei tried to defeat Ken-Oh while mounted on Kokuoh but failed when his Shinketsushuu Hiko was struck. When Kenshiro stood up to fight his adoptive brother, he gave Kokuoh a blow to the face hard enough force the conqueror to dismount. During the war with Souther's empire, Kokuoh and Ken-Oh appear to make sure Kenshiro dies in battle, but not after killing some of the Holy Imperial forces. It was shown that Raoh could use him to crush anyone not worthy of dying by his fists when he kills some deserters. In the Goshasei arc, Juza stole the black horse. this resulted in Raoh being unable to move until he saw his horse again. Juza then returned Kokuoh to his master before the rematch. In the aftermath, Kokuoh gave his second man to ride him a proper burial. Once Raoh lost his final battle against Kenshiro, the latter inherited the horse as his new mount. During untold years, Kokuoh lost one of his eyes. The giant horse stayed behind on the mainland while Kenshiro set out for the land of Asura to save Rin. Sometime later, Bat rode him to Asura. After the battle with Kaioh, Kokuoh reunited with Kenshiro. During a thunderstorm that took Kenshiro's memory, Kokuoh died peacefully.
In the spinoff prequel, Kokuoh was a leader of a herd of wild horses before being tamed by Raoh as his own.