Suddenly 4 People in the Family?!

Miyu Kōzuki'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.