Nobita keeps dreaming of a boy named Ropporu and his companion Chammy fleeing through space, until one night his room shakes and Chammy forces open a passage in his floor. A malfunction has linked their spaceship to Nobita's bedroom, and through it Nobita and Doraemon reach Ropporu's frontier world. There the difference in gravity makes the two of them far stronger than usual, which matters once agents of a mining company start harassing Ropporu's family and neighbors to seize the planet's resources.