Miyu KĊzuki's parents had moved to the United States to work for NASA. Miyu has been told she is to live with her parents' old friend. She arrives, and it turns out to be a Buddhist temple. She meets her parents' friend, the temple monk, Hoshou Saionji, and his teenaged son, Kanata. The monk soon leaves for India for religious training, leaving Miyu behind with Kanata. Shortly after, a UFO flies into the house, and inside were an alien baby called Ruu and a "sitter-pet" called Wanya. They all then decide to live in the temple together. Kanata peeps at Miyu while she's showering, just as Miyu has seen him changing.
It was Miyu's first day at her new school. She finds out that Kanata has a fan club, and he is the class president. Miyu meets Christine Hanakomachi, a half-French girl who fancies Kanata. During class, Miyu spots Ruu flying outside. Kanata and Miyu chase after Ruu. Ruu ends up climbing a chimney, forcing Kanata and Miyu to climb it too.
Chris and her friends came by Kanata's house to have a welcome party for Miyu. But their home turned out to be a disaster. They needed to take down floating items and hide Ruu and Wanya from their guests. Chris misunderstands Miyu and Kanata's relationship, after they discover Ruu.
Kanata and Miyu both go out with their friends. Before Miyu leaves, she notices that her necklace is missing. A crow has taken it. But 3 year-old Momoka chases the crow away and retrieves the necklace. While shopping for dinner, Wanya loses Ruu. Ruu finds Momoka with the necklace. They both are together, when finally Kanata and Miyu find Momoka and Ruu. Momoka starts referring to Ruu as her boyfriend.