Monchichi-chan, the twin sister, loves her twin brother very much. She is a pretty crybaby and always follows her brother. Monchichi-kun, the twin brother, protects his sister. He is a brave adventurer and a fishing champion but sometimes becomes a hasty boy. They enjoy wonderful and mysterious adventures together everyday. When they take a space walk, they ride on a swan of the swan constellation and build a small house with aliens in the space. They can do everything children want to do and dream of. This heartwarming animation series featuring the pretty twins surely gives wonderful dreams, brother-sister love and hopes for the future to all the children in the world.