Cheon Yeo-woon is an illegitimate prince of the Great Heavenly Demonic Cult, born without the support of the powerful Six Clans. After his mother is murdered and his life is threatened by his half-siblings, he is visited by a descendant from the far future. This descendant injects Yeo-woon with a "Nano Machine"—a 7th-generation AI from the future that can scan techniques, heal wounds, and simulate combat in real-time. With the power of future technology in a world governed by martial arts, Yeo-woon begins his bloody ascent to become the "Heavenly Demon" and exact vengeance on those who destroyed his family.