Doraemon Movie 21: Nobita no Taiyou Ou Densetsu

Doraemon and his friends accidentally open a passage through time and arrive in Mayana, a jungle kingdom inspired by an ancient civilization. There Nobita meets Prince Tio, the heir to the throne, who looks almost exactly like him but possesses the confidence and discipline Nobita lacks.

The two boys decide to exchange places and experience each other's lives. Their game quickly becomes dangerous because Mayana is threatened by the witch Ledina, whose curse hangs over the royal family and the kingdom itself. As Doraemon's group becomes involved, Nobita must do more than imitate a prince: he has to help Tio defend his people and prove that courage is not determined by appearance.