Queen Millennia

The story takes place in 1999, where Amamori Hajime, an elementary school student, is trying to balance school and social life after his house is destroyed in an accident involving his father's experimental equipment. He moves in with his uncle, an astronomer, and befriends Yayoi Yukino, his uncle's assistant at the observatory. Yayoi is revealed to be the Millennial Queen, chosen by her home planet LaMetal to help prepare for a potential disaster that will occur when LaMetal's highly elliptical orbit sends it close to Earth every 1000 years.