Sun Wukong has guarded the Southern Heavenly Gate for five hundred years. During that time, the gods of Heaven have never seen a demon, so they believe that demons do not exist and that Sun Wukong fabricated their existence to monopolize the Southern Heavenly Gate and seize the divine treasure hidden within. Forced to leave, Sun Wukong immediately becomes the target of fierce competition among the forces of the Three Realms, including the Western Spirit Mountain, the Kingdom of Women, and the Demon Alliance of Beiju Luzhou. The demon race celebrates its opportunity, and the Demon Ancestor Luo Hou orders demons throughout the Three Realms to assemble and launch a massive assault on Heaven, plunging all three realms into war. To protect all living beings, Sun Wukong resolves to shield ordinary mortals from the demons' invasion.