Liu Er agreed to the demon king, pretending to be Sun Wukong and destroying Tang Monk's plan to obtain scriptures, in order to save the female demon wisteria who was injured by Sun Wukong. To prove their identity, Liu Er and Sun Wukong repeatedly dueled, but it was difficult for everyone to distinguish which was true and which was false.Gradually, Liu Er also forgot his identity and firmly believed that he was Sun Wukong. In order to ensure the peace of all beings, Liu Er ultimately chose to fight alongside Sun Wukong, even willing to sacrifice himself