One day Doraemon, Nobita, Shizuka, Gian and Suneo were shooting a film as space heroes. When they were shooting the film in the open lot a boy called Aron comes and alerts them of aliens attacking his planet. They agree to help him by turning into real superheroes, but it isn't as easy as it looks.
Shimajiro, who helped an injured baby whale Kuu-chan, takes care of Kuu-chan who wants to return to her mother and keeps her in touch. In order to return Ku-chan, who was about to be sent to the aquarium, to her mother, Shimajiro rides on her back and sets out on a journey toward the southern sea.
