In the year 1999, young student Amamori Hajime's life takes a drastic turn when a mysterious explosion leaves him orphaned. Taken in by his astronomer uncle, he meets Yukino Yayoi, a girl with a secret identity as the Millennial Queen from the planet LaMetal. Yayoi's mission on Earth is to avert a catastrophic event caused by LaMetal's proximity every millennium. While Yayoi aims to save humanity, she faces opposition from the leader of the Millennial Thieves who seeks to thwart her plans. As the mystery unfolds, questions arise about the true intentions of those involved and the imminent threat looming over both planets.