Welcome to the Center of the Earth (Part 1)

Nobita discovers a cave in the mountain, believing it leads to the Earth's core, only to be mocked by Suneo. Nobita is angry, so Doraemon produces the "Heterodox Club Badge," claiming that those who wear it can see a different world (decided by speaking into the microphone). Nobita experiences theories such as the flat Earth theory and the existence of people on the far side of the moon. Then they enter the world of the hollow Earth theory. They sculpte underground people from clay at the Earth's core, name them "Pyron," and help them develop civilization. With Nobita and his friends' help, they use fire, forge weapons, and even build houses, their civilization constantly evolving. After some time, they invite Shizuka over. The monster also wants to make peace, but because it can't speak, it isn't accepted.