A mysterious comet appears around the moon, and a young astronomer witnesses the event and obtains a fragment of the comet after it lands nearby. However, he is quickly discredited by the scientific community, including his girlfriends, an astronaut-in-training. The comet, however, is no normal it her own eternally icy paradise. And meanwhile, Luna, the feline advisor of the Scouts, must sort out her own feelings as she finds herself falling for the idealistic astronomer after he saves her life. As Kaguya's minions freeze the streets of Tokyo, the Sailor Soldiers must solve the mystery of the comet and defeat this latest threat to Earth's existence.