The ultimate secret technique of Hokuto Shin Ken. It is said that only one who embraces the true nature of sorrow can awaken its power. Kenshirō was the first man in Hokuto Shin Ken's 1800 year history to learn Musō Tensei during the epic struggles against his friends and great rivals. Musō Tensei allows the user to achieve a state of "nothingness", impervious to physical attacks, and commune with the souls of fallen rivals (Toki, Ryūga, the Nanto Roku Seiken and later Raoh).
Raoh also learned Musō Tensei when his feelings for Yuria unlocked the profound sadness within his heart.
Kaioh was able to negate the power of Musō Tensei with his demonic aura (Matōki) and with the distortional nature of his ultimate technique Anryu Tenha, until Kenshirō absorbed the secrets of Hokuto Sōke and perfected the technique.