Nobita tries to prove the existence of the Monkey King, so he and his friends travel back to the time when Sanzo began his pilgrimage. Doraemon brings a virtual video‑game console and lets Nobita play “Journey to the West,” outfitting him in the Monkey King’s clothes. However, Nobita fails to demonstrate the Monkey King’s existence. While playing the game, the group completes it without battling any demons. Later, they discover that their world is ruled by demons. The problem is that Doraemon left the game console open in the past, allowing demons to manifest and invade the present. Now Doraemon and his friends must return to the past to vanquish the demons.