だぁ！ だぁ！ だぁ！

Miyu is sent to live at a temple with Kanata after her mother leaves for astronaut training and her father goes abroad. The adults soon leave the two junior high students without supervision. A UFO crashes nearby, leaving an alien baby and a sitter stranded with them. The baby treats Miyu and Kanata like parents while they try to keep the situation hidden. Their ordinary school days become a secret household built around caring for a child from space.