Kaio, eldest brother of Raoh, Toki, and Sayaka from the Ryou lineage, was born into servitude to the Hokuto Soke Clan at Taiseiden. Early on, he voiced doubts about their blind service to Raoh. A devastating fire at Taiseiden proved pivotal; witnessing his mother sacrifice herself to save two Hokuto Soke infants deeply traumatized him. Her final words, reinforcing their purpose to serve Hokuto Soke, only hardened his resentment. Kaio stole her body for a secret burial and vowed devotion to evil to shield himself from pain, symbolically severing his humanity by killing his pet dog. He trained relentlessly in martial arts, rising to prominence among his peers until Master Jukei, concerned for Hyoh's weakness, blackmailed him into losing a match. Forced to throw the fight by falling from a bridge, Kaio lost all respect and nurtured a burning hatred for Hokuto Soke. Separated from his brothers during the Land of Shura's invasion, Kaio trained under Jukei alongside Hyoh and Han in Hokuto Ryū Ken. He brutalized Hyoh, nearly killing him before using Hokuto Ryū Ken to brainwash him, erasing memories of Kenshiro and implanting false memories of Kaio and Han as his brothers. Kaio later conquered Shura, ruling as its First Rashō. His appearance features an iron helmet concealing his face initially, later revealing a distinctive "⅄"-shaped scar and a resemblance to Raoh. Kaio's personality centers on embracing evil and eradicating love, a direct result of his mother's death. He blames Hokuto Soke for her loss and his own humiliations, wielding Hokuto Ryū Ken to destroy Hokuto Shinken's legacy. He murdered his sister Sayaka to frame Kenshiro, aiming to provoke mutual destruction between Kenshiro and Hyoh. Exhibiting sadism, he tortured Kenshiro and manipulated Lin's emotions using pressure points to mock love, while paradoxically maintaining reverence for his mother's tomb. Defeated by Kenshiro, he reconciled with Hyoh, expressing regret and accepting death while wishing for rebirth as normal siblings. Kaio mastered Hokuto Ryū Ken, becoming its strongest practitioner. His signature Matōki aura manifested as a visible demonic figure, enabling energy projectiles, defensive shields, and area attacks. He could disrupt Musou Tensei and levitate opponents using Anryu Tenha. His pressure point expertise allowed destructive or manipulative effects. In the Land of Shura arc, Lin's kidnapping by Jask/Taiga drew Kenshiro into conflict with Kaio. After Han's defeat, Kaio confronted Kenshiro to prove Hokuto Ryū Ken's supremacy. Kenshiro's victory led to Kaio's reconciliation with Hyoh and their deaths in a lava flow, their bodies forming an embracing statue.