The Lustrous, a life form of humanoid embodiments of gemstones, fight against the Lunarians, who seek to harvest them for jewellery on the moon. The Lustrous' master, Kongō, assigns one of the weaker jewels, Phos, to assemble a natural history since they are unsuited for battle. Struggling to find new information to include in it, Phos is recommended to seek out the nightwatch, a Lustrous named Cinnabar, whose body carries a powerful poison...