Doraemon Movie 09: Nobita no Parallel Saiyuuki

Nobita wants to prove that the legendary Monkey King really existed, so Doraemon takes the group back to the era of Xuanzang's journey west. To make his claim convincing, Nobita borrows a virtual-reality game based on Journey to the West, but a careless mistake leaves its gate open in the past.

When they return home, the familiar world has changed into a place ruled by demons. Realizing that creatures from the game escaped into history and altered the future, Doraemon and his friends travel back once more, assume the roles of the famous pilgrims, and set out to stop the demons before the corrupted timeline becomes permanent.