Complex sentence: Miki is Miyu's astronaut mother who is obsessed with anything connected to outer space and is hired by NASA, along with her husband, Yu, at the beginning of the story, thus having to leave for the United States.
Split into simpler sentences: Miki is Miyu's astronaut mother, who is obsessed with anything connected with outer space. She is hired by NASA (with her husband, Yu) at the beginning of the story, and must leave for the United States.