Nobita trips into Journey to the West expecting a game, then watches it become real when he breezes through without fighting a single demon. The world he returns to isn't his anymore, it's ruled by the creatures he was supposed to face. A time-travel mess that turns a classic adventure inside out, leaving Doraemon stranded with a kid who has to learn what happens when you skip the hard part.

Nobita is determined to prove that the Monkey King was real, so he and his friends travel back to the moment Sanzo set out on his pilgrimage. Doraemon lets Nobita play a Journey to the West virtual game, which outfits him in the Monkey King's clothing, but his attempt at proof falls flat. After the group finishes the game without battling a single demon, they discover that their own world is now ruled by demons. The cause is that Doraemon left the console running in the past, allowing demons to emerge and invade. Doraemon and the others must head back in time to defeat them in this fantasy film.