Edited version for theaters of the eponymous 1972 show, about Triton, a sole survivor who seeks vengeance against evil sea demigod Poseidon and his monsters who eradicated his clan of good mermen and usurped their throne.
Nobita has to make a diary and record some multilevel process as a school project for holidays. He with the help of Doraemon, creates a new world and embarks an adventurous journey with his friends.