Big Head Son, who has a dream of space travel, meets a special "alien friend" by chance. Big Head Son and Marshmallow Sister team up to participate in the Little Astronaut Program and jointly challenge four levels of space missions. Can they win the competition? How did the "alien friend" help the lagging Big Head Son team regain confidence at the critical moment? How will the navigator, Little Head Dad, encourage Big Head Son and his friends to complete the difficult task together? And where did the "alien friend" who has never been made public come from?