Matoki no Aura

Matōki (魔闘気, demonic fighting spirit) is a special type of ki energy used by practitioners of Hokuto Ryū Ken. It grants the user inhuman powers at the cost of consuming their soul, turning them into a 'demon'. Jukei, the former Hokuto Ryūken successor, was once consumed by its power and murdered his wife and child in the ensuing madness, until Ryuken exorcized the curse.

Kaioh wears a special suit of armor which allows him to focus his evil aura. He used this negative energy to negate Musō Tensei during his first fight with Kenshirō.

Hyo was corrupted by his matōki after the death of his fiancée, Sayaka, which Kaioh framed on Kenshiro in order to unleash Hyo's madness.