Nobita, Gian, Shizuka, and Suneo are getting ready for a school production of “Journey to the West.” As they debate over who should portray the Monkey King, Nobita proposes that the actual Monkey King should take on the role. Since the Monkey King is merely a myth, Nobita and Doraemon decide to travel back in time using a time machine to create a fake one to convince Gian, Shizuka, and Suneo of their idea. However, Doraemon’s machine inadvertently brings fictional monsters into the real world, leading to the downfall of humanity and transforming the future (Nobita’s era) into a world dominated by demons. To undo this catastrophe, Doraemon and his friends must journey back in time to recapture the demons and return them to the machine. Along the way, they encounter a real monk and a child named Rinrei. Ultimately, with the assistance of Dorami, they either return the demons to the machine or eliminate them, restoring the future to its original state.