Because the monkey king is only a legend, Nobita and Doraemon have decided to go back in time using the time machine and make a fake one and show Gian, Shizuka, and Suneo to prove that they are right.

Nobita and his friends under the waters of the Pacific Ocean. Gian and Suneo take Doraemon's underwater vehicle and travel through the Atlantic Ocean, trying to find a treasure ship. Along the way ...