Nobita asks Doraemon for the Moshimo-box and wishes for a world where magic is real. In that new reality, sorcery takes the place of science and technology, and everyone relies on it in everyday life—except Nobita, who, as always, struggles to cast even the simplest spells. Frustrated, he decides to change things back, only to discover that his mother has already thrown the Moshimo-box away.
One day, Doraemon and his friends meet Professor Mangetsu, a researcher of magic and magical creatures like goblins, along with his daughter Miyoko. The professor warns them that the "star of the Underworld" is dangerously approaching Earth's orbit.
With the fate of the planet hanging in the balance, the group must journey to the Underworld and strike the heart of the Underworld King with a silver dart, just as described in the ancient text "The Chronicles of the Underworld". However, their efforts are foiled, and Miyoko is taken captive.
Doraemon and his friends then decide to use the Time Machine to go back to the past. With Dorami's Moshimo-box, they succeed in restoring the Earth. Yet the events unfolding in the Underworld continue to occur within a Parallel Universe, where Miyoko remains a prisoner. As a result, the group is compelled once more to travel to the Underworld and put an end to its oppressive ruler for good.