Ziteng was hurt by Wukong. To save her, Liu Er promised the Devil he would use Wukong’s identity and abort the pilgrimage. His fights against Wukong came to draws and nobody could tell who the right monkey was. Liu Er got lost in mind and believed he was Wukong. For the peace of the world, he had to fight side by side with Wukong even at the price of his life.
