Ryu Hayabusa, the world's most formidable ninja, receives a direct challenge to travel to London and face an enigmatic alchemist terrorist known only as the Regent of the Mask. When their initial confrontation goes awry, the Regent curses Ryu's arm with dark magic that grows stronger by feeding on his accumulated kills, slowly draining his life force. Before vanishing, the masked villain broadcasts an ultimatum to the international community: surrender within days or face annihilation. Compelled by both a personal vendetta and global catastrophe, Ryu pursues the Regent and his faction across multiple continents, racing against time while battling the supernatural corruption consuming his own body.