Matōki no Aura (魔闘気のオーラ, Demonic Fighting Spirit Aura)
Matōki is a special type of ki energy used by practitioners of Hokuto Ryūken. It grants the user inhuman powers at the cost of consuming their soul, turning them into a 'demon' (魔神, Majin). Jukei, the former Hokuto Ryūken successor, was once overwhelmed by its power and murdered his wife and child in a bloody frenzy, until Ryuken defeated him and exorcized the curse.
Kaioh wears a special suit of armor which allows him to focus his evil aura. He used this negative energy to counteract Musō Tensei during his first fight with Kenshiro. Kaioh later killed his own sister, Sayaka, and framed her murder on Kenshiro in order to unleash Hyo's matōki.